Add missing headers() function to restangular's IResponse

restangular/restangular-tests.ts

@@ -92,7 +92,8 @@ myApp.controller('TestCtrl', (
   Restangular.setMethodOverriders(["put", "patch"]);
 
   Restangular.setErrorInterceptor(function (response) {
-      console.error('' + response.status + ' ' + response.data);
+      let location: string = response.headers('Location');
+      console.error('' + response.status + ' ' + response.data + ' ' + location);
   });
 
   Restangular.setRequestSuffix('.json');