AFHTTPRequestOperation *op = [manager GET:@"http://www.github.com" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSLog(@"%@",[[NSString alloc]initWithData:responseObject encoding:NSUTF8StringEncoding]);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {

    }];

AFNetworking可以通过这个方式来发送get请求，如何在这种方式下设置cachePolicy