title: Parse unknown JSON key with Moshi
body: <p>I'm trying to parse a JSON I know almost nothing about.</p>
  
  <p>Example of a JSON response</p>
  
  <pre><code>{
      "response": {
         "content":{
              "xxxxxx": "xxxxx",
              "xxxxx": "xxxxxx",
              ...... indeterminate times
          }
      }
  }
  </code></pre>
  
  <p>I tried to create an adapter, but nothing works :</p>
  
  <pre class="lang-java prettyprint-override"><code>@FromJson
  fun fromJson(json: Map&lt;String, String&gt;): MyResponse {
      Log.d("JSON", json.toString())
      return MyResponse(...)
  }
  </code></pre>
  
  <p>Is it possible to achieve this with Moshi? If so, what should I do?</p>