Fixed misusage of `initialize` function

MJRefresh/UIScrollView+MJExtension.m

@@ -16,7 +16,7 @@ @implementation UIScrollView (MJExtension)
 
 static BOOL respondsToAdjustedContentInset_;
 
-+ (void)initialize
++ (void)load
 {
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{