Import event-target-shim npm module

Reviewed By: @foghina

Differential Revision: D2498747

Author: vjeux

npm-shrinkwrap.json

@@ -52,6 +52,7 @@
     "chalk": "^1.1.1",
     "connect": "^2.8.3",
     "debug": "^2.2.0",
+    "event-target-shim": "^1.0.5",
     "fbjs-scripts": "^0.2.1",
     "graceful-fs": "^4.1.2",
     "image-size": "^0.3.5",