Fixes CGBitmapContextCreate unsupported parameter error visible in iOS7.

Fixes `CGBitmapContextCreate` param type error visible in `iOS 7` when running test JS projects (tested w/ Developer Preview for iPhone/XCode5):

```
Jun 10 ##:##:## XXX.local YYY[58909] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component color space; kCGImageAlphaPremultipliedLast; 722 bytes/row.
```

- Reference: [Image resized error: CGBitmapContextCreate: unsupported parameter](http://stackoverflow.com/questions/2235210/image-resized-error-cgbitmapcontextcreate-unsupported-parameter)