fix error with formParams in async ops

Author: cbornet

modules/swagger-codegen/src/main/resources/Java/libraries/retrofit/api.mustache

@@ -34,8 +34,8 @@ public interface {{classname}} {
 {{/allParams}}   * @param cb callback method   
    * @return void
    */
-  {{#libraries/retrofit/formParams}}{{#-first}}
-  {{#isMultipart}}@Multipart{{/isMultipart}}{{^isMultipart}}@FormUrlEncoded{{/isMultipart}}{{/-first}}{{/libraries/retrofit/formParams}}
+  {{#formParams}}{{#-first}}
+  {{#isMultipart}}@Multipart{{/isMultipart}}{{^isMultipart}}@FormUrlEncoded{{/isMultipart}}{{/-first}}{{/formParams}}
   @{{httpMethod}}("{{path}}")  
   void {{nickname}}(
     {{#allParams}}{{>libraries/retrofit/queryParams}}{{>libraries/retrofit/pathParams}}{{>libraries/retrofit/headerParams}}{{>libraries/retrofit/bodyParams}}{{>libraries/retrofit/formParams}}, {{/allParams}}Callback<{{#returnType}}{{{returnType}}}{{/returnType}}{{^returnType}}Object{{/returnType}}> cb

samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/api/PetApi.java

@@ -168,6 +168,7 @@ Void updatePetWithForm(
    * @return void
    */
 
+  @FormUrlEncoded
   @POST("/pet/{petId}")  
   void updatePetWithForm(
     @Path("petId") String petId, @Field("name") String name, @Field("status") String status, Callback<Void> cb
@@ -227,6 +228,7 @@ Void uploadFile(
    * @return void
    */
 
+  @Multipart
   @POST("/pet/{petId}/uploadImage")  
   void uploadFile(
     @Path("petId") Long petId, @Part("additionalMetadata") String additionalMetadata, @Part("file") TypedFile file, Callback<Void> cb