Remove dispatch_release when iOS >= 6 || OSX >= 1080

Calling dispatch_release is forbidden under ARC in new iOS and OSX versions.

This preprocessor macro might help:

#define YourDispatchQueueRelease(q) (dispatch_release(q))
#if TARGET_OS_IPHONE
    #if __IPHONE_OS_VERSION_MIN_REQUIRED >= 60000
        #define YourDispatchQueueRelease(q)
    #endif
#else
    #if MAC_OS_X_VERSION_MIN_REQUIRED >= 1080
        #define YourDispatchQueueRelease(q)
    #endif
#endif

References:
https://github.com/ccgus/fmdb/commit/aef763eeb64e6fa654e7d121f1df4c
https://github.com/magicalpanda/MagicalRecord/pull/260