Upgrade uglify

Author: anttiai

package.json

@@ -47,7 +47,7 @@
     "fetch-mock": "^7.3.3",
     "mocha": "^5.0.5",
     "node-fetch": "^2.5.0",
-    "uglify-js": "1.3.5",
+    "uglify-js": "^3.5.15",
     "webpack": "^4.4.1",
     "webpack-cli": "^2.0.13"
   }