Update dependency mini-css-extract-plugin to v2

Author: renovate[bot]

package.json

@@ -74,7 +74,7 @@
     "istanbul-reports": "3.0.2",
     "jest-puppeteer-istanbul": "0.5.3",
     "jest-silent-reporter": "0.3.0",
-    "mini-css-extract-plugin": "1.2.1",
+    "mini-css-extract-plugin": "2.9.4",
     "minimist": "1.2.5",
     "npm-run-all": "4.1.5",
     "null-loader": "4.0.1",