Remove grunt + updates dependencies

[anselmbradford]

Fixes https://github.com/cfpb/generator-cf/issues/141

Removals

• Removes grunt workflow.

Changes

• Updates browser-sync, gulp-autoprefixer, gulp-eslint, gulp-less, gulp-sourcemaps, http-server, require-dir, uglifyjs-webpack-plugin, and webpack-stream.

Testing

• Follow the testing instructions in https://github.com/cfpb/generator-cf#contributing

[Scotchester]

Oh, I also thought maybe we handle the release commit separately after we finish with all of these little updates.

[jimmynotjim]

Oh good point. There's a lot of unreleased in the changelog so this is the perfect time for a major release.