refactor(angular.copy): use array.length=0 to empty arrays

src/Angular.js

@@ -567,9 +567,7 @@ function copy(source, destination){
   } else {
     if (source === destination) throw Error("Can't copy equivalent objects or arrays");
     if (isArray(source)) {
-      while(destination.length) {
-        destination.pop();
-      }
+      destination.length = 0;
       for ( var i = 0; i < source.length; i++) {
         destination.push(copy(source[i]));
       }