Warning that ProgressBarAndroid is deprecated

[Frangeris Peguero]

Thank's for this pack, awesome :)

I'm receiving a warning:

Circular indeterminate `ProgressBarAndroid`is deprecated. Use `ActivityIndicator` instead.

Android 4.2.2
"react-native": "^0.31.0",
"react": "^15.2.1",

Is it time to upgrade the src/ProgressBar.js?

[CoteViande]

#17