Fix Xcode6 unknow type CGFloat and NSString

MJRefreshExample/MJRefreshExample/MJRefresh/MJRefreshConst.m

@@ -6,6 +6,8 @@
 //  Copyright (c) 2014年 itcast. All rights reserved.
 //
 
+#import <UIKit/UIKit.h>
+
 const CGFloat MJRefreshViewHeight = 64.0;
 const CGFloat MJRefreshFastAnimationDuration = 0.25;
 const CGFloat MJRefreshSlowAnimationDuration = 0.4;