feat(package.json): Update dependency mini-css-extract-plugin to v0.12.0

Author: renovate-bot

package.json

@@ -44,7 +44,7 @@
     "fs-extra": "6.0.1",
     "html-webpack-plugin": "4.5.0",
     "http-proxy-middleware": "0.21.0",
-    "mini-css-extract-plugin": "0.11.3",
+    "mini-css-extract-plugin": "0.12.0",
     "minimist": "1.2.5",
     "object-assign": "4.1.1",
     "optimize-css-assets-webpack-plugin": "5.0.3",