Fix TypeScript typings

I'm not sure why it wasn't like this but typescript needs it to be like this in order to work. Without this change it just gives errors.

Author: Gerharddc

src/index.d.ts

@@ -3,7 +3,7 @@
 // Definitions by: Kyle Roach <https://github.com/iRoachie>
 // TypeScript Version: 2.3.2
 
-import React from 'react'
+import * as React from 'react'
 import { ViewStyle } from 'react-native'
 
 interface DateTimePickerProps {