fixed typo. in typescript generator api template

Author: HugoMario

src/main/resources/handlebars/typescript-fetch/api.mustache

@@ -61,7 +61,7 @@ export class BaseAPI {
  * @extends {Error}
  */
 export class RequiredError extends Error {
-    name: "RequiredError"
+    name = "RequiredError"
     constructor(public field: string, msg?: string) {
         super(msg);
     }