add scalar converter to retrofit2

Fix #2177

modules/swagger-codegen/src/main/resources/Java/libraries/retrofit2/ApiClient.mustache

@@ -12,8 +12,9 @@ import org.apache.oltu.oauth2.client.request.OAuthClientRequest.TokenRequestBuil
 
 import retrofit2.Converter;
 import retrofit2.Retrofit;
-import retrofit2.converter.gson.GsonConverterFactory;
 {{#useRxJava}}import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory;{{/useRxJava}}
+import retrofit2.converter.gson.GsonConverterFactory;
+import retrofit2.converter.scalars.ScalarsConverterFactory;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -120,6 +121,7 @@ public class ApiClient {
                 .baseUrl(baseUrl)
                 .client(okClient)
                 {{#useRxJava}}.addCallAdapterFactory(RxJavaCallAdapterFactory.create()){{/useRxJava}}
+                .addConverterFactory(ScalarsConverterFactory.create())
                 .addConverterFactory(GsonCustomConverterFactory.create(gson));
     }
 

modules/swagger-codegen/src/main/resources/Java/libraries/retrofit2/build.gradle.mustache

@@ -103,6 +103,7 @@ ext {
 
 dependencies {
     compile "com.squareup.retrofit2:retrofit:$retrofit_version"
+    compile "com.squareup.retrofit2:converter-scalars:$retrofit_version"
     compile "com.squareup.retrofit2:converter-gson:$retrofit_version"
 {{#useRxJava}}
     compile "com.squareup.retrofit2:adapter-rxjava:$retrofit_version"

modules/swagger-codegen/src/main/resources/Java/libraries/retrofit2/pom.mustache

@@ -118,6 +118,11 @@
       <artifactId>retrofit</artifactId>
       <version>${retrofit-version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.squareup.retrofit2</groupId>
+      <artifactId>converter-scalars</artifactId>
+      <version>${retrofit-version}</version>
+    </dependency>
     <dependency>
       <groupId>com.squareup.retrofit2</groupId>
       <artifactId>converter-gson</artifactId>