fix(api_docs): slightly more accurate description of TS overrideOnEventDone

modules/angular2/src/core/zone/ng_zone.ts

@@ -86,8 +86,8 @@ export class NgZone {
   }
 
   /**
-   * Sets the zone hook that is called immediately after the last turn in the
-   * current event completes. At this point Angular will no longer attempt to
+   * Sets the zone hook that is called immediately after the last turn in
+   * an event completes. At this point Angular will no longer attempt to
    * sync the UI. Any changes to the data model will not be reflected in the
    * DOM. {@link onEventDoneFn} is executed outside Angular zone.
    *