fix(package): update file-loader to version 4.0.0

Author: greenkeeper[bot]

packages/core/package.json

@@ -7,7 +7,7 @@
     "babel-loader": "^8.0.2",
     "copy-webpack-plugin": "^4.5.2",
     "css-loader": "^1.0.0",
-    "file-loader": "^3.0.0",
+    "file-loader": "^4.0.0",
     "html-webpack-plugin": "^3.2.0",
     "lodash.merge": "^4.6.1",
     "mini-css-extract-plugin": "^0.4.3",