title: String not being passed as query in retrofit 2.0
body: <p>I am having problem sending string parameters as query using @Field("test")
  It works with Integer</p>
  
  <pre><code>@FormUrlEncoded
  @POST("/yokitab/forum.php")
  Call&lt;List&lt;QuestionData&gt;&gt; getQuestions(
          @Field("id") int id,
  ); 
  </code></pre>
  
  <p>works</p>
  
  <pre><code>@FormUrlEncoded
  @POST("/yokitab/forum.php")
  Call&lt;List&lt;QuestionData&gt;&gt; getQuestions(
          @Field("question") String ques
  );
  </code></pre>
  
  <p>doesn't work</p>