Merge pull request facebook#3662 from zpao/update-uglify

Update uglify dependency

Author: zpao

package.json

@@ -61,7 +61,7 @@
     "sauce-tunnel": "~1.1.0",
     "tmp": "~0.0.18",
     "typescript": "^1.4.0",
-    "uglify-js": "~2.4.0",
+    "uglify-js": "^2.4.20",
     "uglifyify": "^3.0.1",
     "wd": "~0.2.6"
   },