refactor(ngOptions): access copy() directly (angular.copy --> copy)

Author: gkalpak

src/ng/directive/ngOptions.js

@@ -399,7 +399,7 @@ var ngOptionsDirective = ['$compile', '$document', '$parse', function($compile,
           getViewValueFromOption: function(option) {
             // If the viewValue could be an object that may be mutated by the application,
             // we need to make a copy and not return the reference to the value on the option.
-            return trackBy ? angular.copy(option.viewValue) : option.viewValue;
+            return trackBy ? copy(option.viewValue) : option.viewValue;
           }
         };
       }