build: Bump mime and url-loader (#403)

Removes [mime](https://github.com/broofa/mime). It's no longer used after updating ancestor dependency [url-loader](https://github.com/webpack-contrib/url-loader). These dependencies need to be updated together.


Removes `mime`

Updates `url-loader` from 0.5.9 to 4.1.1
- [Release notes](https://github.com/webpack-contrib/url-loader/releases)
- [Changelog](https://github.com/webpack-contrib/url-loader/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/url-loader@v0.5.9...v4.1.1)

---
updated-dependencies:
- dependency-name: mime
  dependency-type: indirect
- dependency-name: url-loader
  dependency-type: direct:development
...

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package.json

@@ -50,7 +50,7 @@
     "sass-loader": "~4.0.2",
     "style-loader": "^0.13.1",
     "text-loader": "0.0.1",
-    "url-loader": "^0.5.7",
+    "url-loader": "^4.1.1",
     "webpack": "^1.13.2",
     "webpack-dev-server": "^1.16.2"
   },