title: Posting Image with array parameters using AFNetworking 2.0 not working
body: <p>I'm trying to post an image with a parameter (categories) that is an array. If I leave this parameter out, I can submit fine. However, if I leave it in, my server throws an error because the array value doesn't seem to be getting serialized correctly.</p>
  
  <pre><code>NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithDictionary:@{
      @"auth_token" : authToken,
      @"title" : title,
      @"categories" : @[1,2,3]
  }];
  
  return [[MyHTTPSessionManager sharedManager] POST:path parameters:dict constructingBodyWithBlock:^(id&lt;AFMultipartFormData&gt; formData) {
      [formData appendPartWithFileData:imageData
                                  name:@"image"
                              fileName:@"image.jpg"
                              mimeType:@"image/jpeg"];
  } success:nil failure:nil];
  </code></pre>
  
  <p>Looking at my server logs, this is how categories is coming across:</p>
  
  <pre><code>Parameters: {"categories"=&gt;"(\n    1,\n    2,\n    3\n)", … }
  </code></pre>
  
  <p>And I need it to look like:</p>
  
  <pre><code>Parameters: {"categories"=&gt;[1,2,3], … }
  </code></pre>
  
  <p>I've tried setting my instance of AFHTTPSessionManager's requestSerializer to <code>[AFJSONRequestSerializer serializer]</code> but that doesn't seem to help.</p>
  
  <p>How can I properly POST an image + parameters? I'd like to avoid falling back to AFHTTPRequestOperation.</p>
  
  <p>Thanks!</p>