Bump mini-css-extract-plugin from 1.3.3 to 1.3.4 (#525)

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 1.3.3 to 1.3.4.
- [Release notes](https://github.com/webpack-contrib/mini-css-extract-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/mini-css-extract-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/mini-css-extract-plugin@v1.3.3...v1.3.4)

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Author: dependabot[bot]

package.json

@@ -22,7 +22,7 @@
     "cross-env": "7.0.3",
     "css-loader": "5.0.1",
     "fibers": "5.0.0",
-    "mini-css-extract-plugin": "1.3.3",
+    "mini-css-extract-plugin": "1.3.4",
     "postcss-loader": "3.0.0",
     "sass": "1.32.4",
     "sass-loader": "10.1.1",