[Scala] Handling map[String, Model] in Scala client generated code

Description

The swagger-codegen generated code for Scala client doesn't handle map[String, SchemaObject]

Swagger-codegen version

<groupId>io.swagger</groupId>
<artifactId>swagger-codegen-maven-plugin</artifactId>
<version>2.2.2</version>

Swagger yaml spec:

        200:
          description: OK
          schema:
            type: object
            additionalProperties:
              $ref: "#/definitions/dataSchema"

Exception:

Exception in thread "main" java.lang.ClassCastException: com.xyz.model.dataSchema cannot be cast to scala.collection.immutable.Map

Fix proposed:
ApiInvoker.scala

case "map" => {
          val typeInfo = mapper.getTypeFactory().constructMapType(classOf[java.util.Map[_,_]], classOf[String], cls);
          println(json)
          val response = mapper.readValue(json, typeInfo).asInstanceOf[java.util.Map[_,_]]
          response.asScala.toMap
        }

Start with ApiInvoker.scala and reproduce the Swagger YAML case where a 200 response is an object with additionalProperties referencing dataSchema. Check the generated Scala client's map deserialization path and verify the result is handled as a Scala map without the ClassCastException; completion should include a passing regression test if the repository provides one.