title: Restkit version 0.20.0-pre2. : Issue:No key in post object.how to post?
body: <p>I have a post request with an array of values as input.The problem is that, the array has no key for values inside to post!.How to set the mapping ?</p>
  
  <p>Have to post this</p>
  
  <pre><code> "group_ids": [
                  "1",
                  "2",
                  "3"
          ]
  </code></pre>
  
  <p>How to map the value and do the post using restkit 2.0</p>