Update dependency mini-css-extract-plugin to v0.12.0

Author: renovate-bot

package.json

@@ -119,7 +119,7 @@
     "jest-fetch-mock": "3.0.3",
     "jsdom": "16.4.0",
     "lint-staged": "10.4.2",
-    "mini-css-extract-plugin": "0.11.2",
+    "mini-css-extract-plugin": "0.12.0",
     "node-sass": "4.14.1",
     "npm-check-updates": "7.1.1",
     "prettier": "2.1.2",