upgrade url loader

Author: jojozhuang

package-lock.json

@@ -33,7 +33,7 @@
     "react-bootstrap": "0.33.1",
     "react-dom": "16.14.0",
     "react-router-dom": "4.3.1",
-    "url-loader": "1.1.2"
+    "url-loader": "4.1.1"
   },
   "devDependencies": {
     "babel-core": "6.26.0",