消息中心UI，逻辑调整 # review by 孙凯

@@ -33,7 +33,7 @@ export default class MessageCell extends Component {
         if (msgNumber <= 0) {
             return null;
         }
-        msgNumber = msgNumber > 9 ? '9+' : msgNumber;
+        msgNumber = msgNumber > 99 ? '99+' : msgNumber;
 
         return (
           <View style={styles.unreadMsgContainer}>
@@ -162,6 +162,7 @@ let styles = StyleSheet.create({
       color: 'white',
       backgroundColor: 'transparent',
       padding: 5,
+      top: -2,
     },
     cellContent: {
       flexDirection: 'column',