fix showDatePicker in ios

Author: WhatAKitty

DateTime.ios.js

@@ -43,7 +43,7 @@ export default class DateTimePicker extends Component {
         this.setState({
             mode: 'date',
             visible: true,
-            date: new Date()
+            date: date
         });
     }
 
@@ -146,4 +146,4 @@ const styles = StyleSheet.create({
         height: 1,
         backgroundColor: '#CCC'
     }
-});
+});