Fix calendar error

Fix calendar error

MJRefresh.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
     s.name         = 'MJRefresh'
-    s.version      = '3.0.1'
+    s.version      = '3.0.4'
     s.summary      = 'An easy way to use pull-to-refresh'
     s.homepage     = 'https://github.com/CoderMJLee/MJRefresh'
     s.license      = 'MIT'

MJRefresh/Custom/Header/MJRefreshStateHeader.m

@@ -55,7 +55,7 @@ - (void)setTitle:(NSString *)title forState:(MJRefreshState)state
 
 #pragma mark - 日历获取在9.x之后的系统使用currentCalendar会出异常。在8.0之后使用系统新API。
 - (NSCalendar *)currentCalendar {
-    if ([NSCalendar instancesRespondToSelector:@selector(calendarWithIdentifier:)]) {
+    if ([NSCalendar respondsToSelector:@selector(calendarWithIdentifier:)]) {
         return [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
     }
     return [NSCalendar currentCalendar];