add missing property targetUrl to InitialConfiguration in stackdriver-errors.d.ts (#99)

Author: toebbel

stackdriver-errors.d.ts

@@ -67,6 +67,11 @@ declare module 'stackdriver-errors-js' {
    * Initial configuration
    */
   interface InitialConfiguration {
+    /**
+     * Overwrite endpoint that errors are reported to.
+     */
+    targetUrl?: string;
+    
     /**
      * The context in which the error occurred
      */