chore(deps): update dependency file-loader to v4 (#1971)

Author: renovate[bot]

package-lock.json

@@ -88,7 +88,7 @@
     "eslint-config-webpack": "^1.2.5",
     "eslint-plugin-import": "^2.18.2",
     "execa": "^1.0.0",
-    "file-loader": "^3.0.1",
+    "file-loader": "^4.0.0",
     "html-loader": "^0.5.5",
     "html-webpack-plugin": "^3.2.0",
     "husky": "^3.0.2",