Repair JSONKit.m file appears in the iOS 6.0 or later version of warning.

The warning at iOS 6.0 or later.


-    array->isa      = _JKArrayClass;
+    object_setClass(array,_JKArrayClass);
-    dictionary->isa      = _JKDictionaryClass;
+    object_setClass(dictionary,_JKDictionaryClass);