错误信息：
*** Collection <__NSDictionaryM: 0x174048c70> was mutated while being enumerated.
日志如下：
Last Exception Backtrace:
0 CoreFoundation 0x184cd02d8 __exceptionPreprocess + 132
1 libobjc.A.dylib 0x1964f40e4 objc_exception_throw + 60
2 CoreFoundation 0x184ccfc8c __NSFastEnumerationMutationHandler + 140
3 vstorelink 0x1004915ec -AVRequestManager jsonForSet:
4 vstorelink 0x100492930 -AVRequestManager allJsonDict
5 vstorelink 0x100492d4c -AVRequestManager jsonForCloud
6 vstorelink 0x10047adc0 -AVObject refreshHasDataForCloud:
7 vstorelink 0x10047ab14 -AVObject refreshHasDataForCloud
8 vstorelink 0x100474ed4 _74-[AVObject saveWithBlock:waitUntilDone:eventually:verifyBeforeSave:error:]block_invoke (AVObject.m:646)
9 libdispatch.dylib 0x196b45994 dispatchcall_block_and_release + 24
10 libdispatch.dylib 0x196b45954 dispatchclient_callout + 16
11 libdispatch.dylib 0x196b4a20c dispatchmain_queue_callback_4CF + 1608
12 CoreFoundation 0x184c877f8 CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 12
13 CoreFoundation 0x184c858a0 __CFRunLoopRun + 1492
14 CoreFoundation 0x184bb12d4 CFRunLoopRunSpecific + 396
15 GraphicsServices 0x18e3c76fc GSEventRunModal + 168
16 UIKit 0x189776fac UIApplicationMain + 1488
17 vstorelink 0x1001b3978 main (main.m:14)
18 libdyld.dylib 0x196b72a08 start + 4
看上去是AVRequestManager在遍历json对象期间，试图修改json对象。
闪退现象偶尔会发生，当打开app的时候，同时收到几个消息，就会出现闪退，请帮忙看一下，是不是AVRequestManager的同步问题。
