Add fixes for es6 generator (#180)

Various fixes for JS (ES6) generator

samples/client/petstore/javascript-es6/src/api/FakeApi.js

@@ -68,7 +68,7 @@ export default class FakeApi {
       let authNames = [];
       let contentTypes = [];
       let accepts = ['*/*'];
-      let returnType = Boolean;
+      let returnType = 'Boolean';
 
       return this.apiClient.callApi(
         '/fake/outer/boolean', 'POST',
@@ -150,7 +150,7 @@ export default class FakeApi {
       let authNames = [];
       let contentTypes = [];
       let accepts = ['*/*'];
-      let returnType = Number;
+      let returnType = 'Number';
 
       return this.apiClient.callApi(
         '/fake/outer/number', 'POST',
@@ -191,7 +191,7 @@ export default class FakeApi {
       let authNames = [];
       let contentTypes = [];
       let accepts = ['*/*'];
-      let returnType = String;
+      let returnType = 'String';
 
       return this.apiClient.callApi(
         '/fake/outer/string', 'POST',

samples/client/petstore/javascript-es6/src/api/Fake_classname_tags123Api.js

@@ -1,82 +0,0 @@
-/**
- * Swagger Petstore
- * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
- *
- * OpenAPI spec version: 1.0.0
- * Contact: apiteam@swagger.io
- *
- * NOTE: This class is auto generated by the swagger code generator program.
- * https://github.com/swagger-api/swagger-codegen.git
- * Do not edit the class manually.
- *
- */
-
-
-import ApiClient from "../ApiClient";
-import Client from '../model/Client';
-
-/**
-* Fake_classname_tags123 service.
-* @module api/Fake_classname_tags123Api
-* @version 1.0.0
-*/
-export default class Fake_classname_tags123Api {
-
-    /**
-    * Constructs a new Fake_classname_tags123Api. 
-    * @alias module:api/Fake_classname_tags123Api
-    * @class
-    * @param {module:ApiClient} [apiClient] Optional API client implementation to use,
-    * default to {@link module:ApiClient#instance} if unspecified.
-    */
-    constructor(apiClient) {
-        this.apiClient = apiClient || ApiClient.instance;
-    }
-
-
-    /**
-     * Callback function to receive the result of the testClassname operation.
-     * @callback module:api/Fake_classname_tags123Api~testClassnameCallback
-     * @param {String} error Error message, if any.
-     * @param {module:model/Client} data The data returned by the service call.
-     * @param {String} response The complete HTTP response.
-     */
-
-    /**
-     * To test class name in snake case
-     * @param {module:model/Client} body client model
-     * @param {module:api/Fake_classname_tags123Api~testClassnameCallback} callback The callback function, accepting three arguments: error, data, response
-     * data is of type: {@link module:model/Client}
-     */
-    testClassname(body, callback) {
-      let postBody = body;
-
-      // verify the required parameter 'body' is set
-      if (body === undefined || body === null) {
-        throw new Error("Missing the required parameter 'body' when calling testClassname");
-      }
-
-
-      let pathParams = {
-      };
-      let queryParams = {
-      };
-      let headerParams = {
-      };
-      let formParams = {
-      };
-
-      let authNames = ['api_key_query'];
-      let contentTypes = ['application/json'];
-      let accepts = ['application/json'];
-      let returnType = Client;
-
-      return this.apiClient.callApi(
-        '/fake_classname_test', 'PATCH',
-        pathParams, queryParams, headerParams, formParams, postBody,
-        authNames, contentTypes, accepts, returnType, callback
-      );
-    }
-
-
-}

samples/client/petstore/javascript-es6/src/api/StoreApi.js

@@ -109,7 +109,7 @@ export default class StoreApi {
       let authNames = ['api_key'];
       let contentTypes = [];
       let accepts = ['application/json'];
-      let returnType = {String: Number};
+      let returnType = {'String': 'Number'};
 
       return this.apiClient.callApi(
         '/store/inventory', 'GET',

samples/client/petstore/javascript-es6/src/api/UserApi.js

@@ -297,7 +297,7 @@ export default class UserApi {
       let authNames = [];
       let contentTypes = [];
       let accepts = ['application/xml', 'application/json'];
-      let returnType = String;
+      let returnType = 'String';
 
       return this.apiClient.callApi(
         '/user/login', 'GET',