dependencies: upgrade npm 6.10.3 -> 6.12.0

This upgrade should be backward compatible, but still suffers form major
vulnerabilities in its https-proxy-agent transitive dependency (see
https://www.npmjs.com/advisories/1184).

Changelog:
- https://github.com/npm/cli/releases

6.12.0 (2019-10-08):
    Now npm ci runs prepare scripts for git dependencies, and respects the
    --no-optional argument. Warnings for engine mismatches are printed again.
    Various other fixes and cleanups.

    BUG FIXES
    890b245dc #252 ci: add dirPacker to options (@claudiahdz)
    f3299acd0 #257 npm.community#4792 warn message on engine mismatch
                   (@ruyadorno)
    bbc92fb8f #259 npm.community#10288 Fix figgyPudding error in npm token
                   (@benblank)
    70f54dcb5 #241 doctor: Make OK more consistent (@gemal)

    FEATURES
    ed993a29c #249 Add CI environment variables to user-agent (@isaacs)
    f6b0459a4 #248 Add option to save package-lock without formatting Adds a new
                   config --format-package-lock, which defaults to true.
                   (@bl00mber)

DEPENDENCIES
    0ca063c5d npm-lifecycle@3.1.4:
        fix: filter functions and undefined out of makeEnv (@isaacs)
    5df6b0ea2 libcipm@4.0.4:
        fix: pack git directories properly (@claudiahdz)
        respect no-optional argument (@cruzdanilo)
    7e04f728c tar@4.4.12
    5c380e5a3 stringify-package@1.0.1 (@isaacs)
    62f2ca692 node-gyp@5.0.5 (@isaacs)
    0ff0ea47a npm-install-checks@3.0.2 (@isaacs)
    f46edae94 hosted-git-info@2.8.5 (@isaacs)

TESTING
    44a2b036b #262 fix root-ownership race conditions in meta-test (@isaacs)

6.11.3 (2019-09-03):
    Fix npm ci regressions and npm outdated depth.

    BUG FIXES
    235ed1d28 #239 Don't override user specified depth in outdated. Restores
                   ability to update packages using --depth as suggested by npm audit. (@G-Rath)
    1fafb5151 #242 npm.community#9586 Revert "install: do not descend into
                   directory deps' child modules" (@isaacs)
    cebf542e6 #243 npm.community#9720 ci: pass appropriate configs for file/dir
                   modes (@isaacs)

    DEPENDENCIES
    e5fbb7ed1 read-cmd-shim@1.0.4 (@claudiahdz)
    23ce65616 npm-pick-manifest@3.0.2 (@claudiahdz)

6.11.2 (2019-08-22):
    Fix a recent Windows regression, and two long-standing Windows bugs. Also,
    get CI running on Windows, so these things are less likely in the future.

    DEPENDENCIES
    9778a1b87 cmd-shim@3.0.3: Fix regression where shims fail to preserve exit
              code (@isaacs)
    bf93e91d8 npm-package-arg@6.1.1: Properly handle git+file: urls on Windows
              when a drive letter is included. (@isaacs)

    BUGFIXES
    6cc4cc66f escape args properly on Windows Bash Despite being bash, Node.js
              running on windows git mingw bash still executes child processes
              using cmd.exe. As a result, arguments in this environment need to
              be escaped in the style of cmd.exe, not bash. (@isaacs)

    TESTS
    291aba7b8 make tests pass on Windows (@isaacs)
    fea3a023a travis: run tests on Windows as well (@isaacs)

6.11.1 (2019-08-20):
    Fix a regression for windows command shim syntax.

    37db29647 cmd-shim@3.0.2 (@isaacs)

v6.11.0 (2019-08-20):
    A few meaty bugfixes, and introducing peerDependenciesMeta.

    FEATURES
    a12341088 #224 Implements peerDependenciesMeta (@arcanis)
    2f3b79bba #234 add new forbidden 403 error code (@claudiahdz)

    BUGFIXES
    24acc9fc8 and 45772af0d #217 npm.community#8863 npm.community#9327 do not
              descend into directory deps' child modules, fix shrinkwrap files
              that inappropriately list child nodes of symlink packages (@isaacs
              and @salomvary)
    50cfe113d #229 fixed typo in semver doc (@gall0ws)
    e8fb2a1bd #231 Fix spelling mistakes in CHANGELOG-3.md (@XhmikosR)
    769d2e057 npm/uid-number#7 Better error on invalid --user/--group configs.
              This addresses the issue when people fail to install binary
              packages on Docker and other environments where there is no
              'nobody' user. (@isaacs)
    8b43c9624 nodejs/node#28987 npm.community#6032 npm.community#6658
              npm.community#6069 npm.community#9323 Fix the regression where
              random config values in a .npmrc file are not passed to lifecycle
              scripts, breaking build processes which rely on them. (@isaacs)
    8b85eaa47 save files with inferred ownership rather than relying on SUDO_UID
              and SUDO_GID. (@isaacs)
    b7f6e5f02 Infer ownership of shrinkwrap files (@isaacs)
    54b095d77 #235 Add spec to dist-tag remove function (@theberbie)

    DEPENDENCIES
    dc8f9e52f pacote@9.5.7: Infer the ownership of all unpacked files in
              node_modules, so that we never have user-owned files in root-owned
              folders, or root-owned files in user-owned folders. (@isaacs)
    bb33940c3 cmd-shim@3.0.0:
        9c93ac3 #2 npm#3380 Handle environment variables properly (@basbossink)
        2d277f8 #25 #36 #35 Fix 'no shebang' case by always providing $basedir
                in shell script (@igorklopov)
        adaf20b #26 Fix $* causing an error when arguments contain parentheses
                (@satazor)
        49f0c13 #30 Fix paths for MSYS/MINGW bash (@dscho)
        51a8af3 #34 Add proper support for PowerShell (@ExE-Boss)
        4c37e04 #10 Work around quoted batch file names (@isaacs)
    a4e279544 npm-lifecycle@3.1.3 (@isaacs):
        fail properly if uid-number raises an error
    7086a1809 libcipm@4.0.3 (@isaacs)
    8845141f9 read-package-json@2.1.0 (@isaacs)
    51c028215 bin-links@1.1.3 (@isaacs)
    534a5548c read-cmd-shim@1.0.3 (@isaacs)
    3038f2fd5 gentle-fs@2.2.1 (@isaacs)
    a609a1648 graceful-fs@4.2.2 (@isaacs)
    f0346f754 cacache@12.0.3 (@isaacs)
    ca9c615c8 npm-pick-manifest@3.0.0 (@isaacs)
    b417affbf pacote@9.5.8 (@isaacs)

    TESTS
    b6df0913c #228 Proper handing of /usr/bin/node lifecycle-path test (@olivr70)
    aaf98e88c npm-registry-mock@1.3.0 (@isaacs)

src/package.json

@@ -49,7 +49,7 @@
     "log4js": "0.6.35",
     "measured-core": "1.11.2",
     "nodeify": "^1.0.1",
-    "npm": "6.10.3",
+    "npm": "6.12.0",
     "object.values": "^1.0.4",
     "request": "2.88.0",
     "resolve": "1.1.7",