upgrade image-size version fix caculate webp image size bugs

Summary:
When I try to use webp for app. But some webp images get an error message `unsupported file type` by image-size@0.3.5.

And I in image-size repo I found a issue https://github.com/image-size/image-size/issues/65.
This is the same problem.

And try image-size^0.5.1 the error fixed.

![image](https://cloud.githubusercontent.com/assets/13161470/23597366/403a3070-026d-11e7-8666-f4357f1eee73.png)
Closes https://github.com/facebook/react-native/pull/14238

Reviewed By: davidaurelio

Differential Revision: D5145534

Pulled By: javache

fbshipit-source-id: a2aeeae19e928ffefbd0b32501d34069ed37386d

package.json

@@ -174,7 +174,6 @@
     "fs-extra": "^1.0.0",
     "glob": "^7.1.1",
     "graceful-fs": "^4.1.3",
-    "image-size": "^0.3.5",
     "inquirer": "^3.0.6",
     "jest-haste-map": "^20.0.4",
     "json-stable-stringify": "^1.0.1",