Summary:
Add one more parameter which can specify the keyboard type of first text input(if exists) to AlertIOS.prompt().
Example usage:
`AlertIOS.prompt('Type a phone number', null, null, 'plain-text', undefined, 'phone-pad')`
Closes https://github.com/facebook/react-native/pull/8781
Differential Revision: D4437900
Pulled By: hramos
fbshipit-source-id: 8141cc0d7c70d13603cd5a1d5ea3f1ab1ce437a6