Fix static 5001 server not starting up

Fix static server that runs on port 5001 not starting up when used in npm start. This would cause a request to the webapp localhost:5000 because it would wait for the assets to load but they would just be pending forever.

It ran fine when running standalone 🤷, npm run gulp -- process:watch:static

From some debugging, it would just get stuck at this line where we import the postcss plugin stack from the styleguide, https://gitlab.com/gitlab-org/gitter/webapp/blob/76fe7110f16cff1d9b53e3dd66399df3b308149b/public/js/webpack.config.js#L8

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It turns on the fix was to update to postcss-import@9.1.0 in @gitterhq/styleguide, https://gitlab.com/gitlab-org/gitter/styleguide/merge_requests/23

I am leaving the other updated dependencies here because they are now updated and confirmed working in the app 👍

Todo

• Wait for https://gitlab.com/gitlab-org/gitter/styleguide/merge_requests/23 to be merged
  • Wait for a new release with those changes, 2.0.0 released 🎉
  • Install new version dependency here