move Toast to oss

Summary: Importing JS changes to fbobjc which should be maintained as a source of truth
for React Native JS files. For more details about this change, please refer to
the original diff in fbandroid repo: D2410797

Reviewed By: @andreicoman11

Differential Revision: D2424679

Libraries/react-native/react-native.js

@@ -39,6 +39,7 @@ var ReactNative = Object.assign(Object.create(require('React')), {
   TabBarIOS: require('TabBarIOS'),
   Text: require('Text'),
   TextInput: require('TextInput'),
+  ToastAndroid: require('ToastAndroid'),
   ToolbarAndroid: require('ToolbarAndroid'),
   TouchableHighlight: require('TouchableHighlight'),
   TouchableNativeFeedback: require('TouchableNativeFeedback'),