Update exception message to use operationId

Update ApiException to use {{operationId}} variable to correct typo

modules/swagger-codegen/src/main/resources/cpprest/api-source.mustache

@@ -344,7 +344,7 @@ pplx::task<{{#returnType}}{{{returnType}}}{{/returnType}}{{^returnType}}void{{/r
         else
         {
             throw ApiException(500
-                , U("error calling findPetsByStatus: unsupported response type"));
+                , U("error calling {{operationId}}: unsupported response type"));
         }
 
         return result;