remove @OverRide from interface method impl

Author: jeffscottbrown

grails-core/src/main/groovy/org/codehaus/groovy/grails/plugins/AbstractGrailsPluginManager.java

@@ -280,7 +280,6 @@ public void shutdown() {
 
     }
 
-    @Override
     public boolean isShutdown() {
         return shutdown;
     }