Bump css-loader from 2.1.1 to 3.4.2

Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 2.1.1 to 3.4.2.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/css-loader/compare/v2.1.1...v3.4.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -30,7 +30,7 @@
     "bluebird": "^3.7.2",
     "bulma": "^0.7.1",
     "co": "~4.6.0",
-    "css-loader": "^2.1.1",
+    "css-loader": "^3.4.2",
     "debug": "^4.1.1",
     "ejs": "^3.0.1",
     "file-loader": "^5.0.2",