Update all Node dependencies, remove unused

[aduth]

Why: Housekeeping in preparation for pending publish, easier future revisions.

There's a few peer dependency mismatches, shown as warnings when installing. It appears these are largely caused by dependencies not being updated yet to allow for newer versions of peer dependencies, but where peer dependencies of more recent versions are not problematic.

Upgrade notes for packages experiencing major version upgrades (possible breaking changes):

autoprefixer 9.6.1 to 10.0.1: https://github.com/postcss/autoprefixer/releases/tag/10.0.0

• Drops support for Node.js (no impact)
• Requires postcss be defined as its own dependency (done)

browserify 16.3.0 to 17.0.0: https://github.com/browserify/browserify/releases/tag/v17.0.0

• Updates dependencies (no impact)

eslint 5.16.0 to 7.11.0: https://github.com/eslint/eslint/releases/tag/v7.0.0, https://github.com/eslint/eslint/releases/tag/v6.0.0
eslint-config-airbnb-base 13.2.0 to 14.2.0: https://github.com/airbnb/javascript/blob/master/packages/eslint-config-airbnb-base/CHANGELOG.md#1400--2019-08-09

• Various new defaults (resolved errors)

gulp-eslint 5.0.0 to 6.0.0: https://github.com/adametry/gulp-eslint/releases/tag/v6.0.0
gulp-if 2.0.2 to 3.0.0: robrich/gulp-if@1b846bb
gulp-stylelint 8.0.0 to 13.0.0: https://github.com/olegskl/gulp-stylelint/releases/tag/v13.0.0, https://github.com/olegskl/gulp-stylelint/releases/tag/11.0.0, https://github.com/olegskl/gulp-stylelint/releases/tag/10.0.0, https://github.com/olegskl/gulp-stylelint/releases/tag/v9.0.0

• Dependency updates, or accounted through transitive dependencies (no impact)

gulp-postcss 8.0.0 to 9.0.0: https://github.com/postcss/gulp-postcss/releases/tag/9.0.0

• Dependency updates (no impact)
• Requires postcss be defined as its own dependency (done)

gulp-rename 1.4.0 to 2.0.0: https://github.com/hparra/gulp-rename/blob/master/CHANGELOG.md#v200

• Breaking change for behavior (not applicable to our usage, no impact)

jest 23.6.0 to 26.5.3: https://github.com/facebook/jest/releases/tag/v26.0.0, https://github.com/facebook/jest/releases/tag/v24.0.0

• Drop Node v8 support (no impact)
• Breaking changes in monorepository packages (not used, no impact)

stylelint 9.10.1 to 13.7.2: https://github.com/stylelint/stylelint/releases/tag/13.0.0, https://github.com/stylelint/stylelint/releases/tag/12.0.0, https://github.com/stylelint/stylelint/releases/tag/11.0.0, https://github.com/stylelint/stylelint/releases/tag/10.0.0

• Forward slashes must be used in globs (not applicable)
• No longer ignores bower_components by default (not applicable)
• Removed createRuleTester API (not applicable)
• Drop Node v8 support (no impact)

wait-on 3.3.0 to 5.2.0: https://github.com/jeffbski/wait-on/releases/tag/v5.0.0, https://github.com/jeffbski/wait-on/releases/tag/v4.0.0

• Rewrites, internal details which would be obviously broken in tests if problematic (not applicable)

[mitchellhenke]

👍🏼 👍🏼

[aduth]

Since I didn't clarify in the original comment: This intentionally doesn't include the USWDS dependency, handled separately in #159 as a larger effort.