feat(package): update clean-css to 4.2.0

Author: joshuawilson

package.json

@@ -107,7 +107,7 @@
     "assets-webpack-plugin": "3.8.4",
     "autoprefixer": "9.0.2",
     "child_process": "1.0.2",
-    "clean-css": "4.1.11",
+    "clean-css": "4.2.0",
     "clean-webpack-plugin": "0.1.19",
     "codelyzer": "4.4.2",
     "copy-webpack-plugin": "4.5.2",