http://www.jianshu.com/p/4bfcae659a44
常用修改方案：
self.acceptableContentTypes = [NSSet setWithObjects:@"application/json", @"text/json", @"text/javascript",@"text/html",@"text/plain",nil];
iOS 使用AFNetworking遇到异常 Request failed: unacceptable content-type: text/html
原文：http://www.cnblogs.com/zbuser/p/5780966.html