refactor(angular.copy): use slice(0) to clone arrays

slice(0) is way faster on most browsers

src/Angular.js

@@ -556,7 +556,8 @@ function copy(source, destination){
     destination = source;
     if (source) {
       if (isArray(source)) {
-        destination = copy(source, []);
+        // http://jsperf.com/copy-array-with-slice-vs-for
+        destination = source.slice(0);
       } else if (isDate(source)) {
         destination = new Date(source.getTime());
       } else if (isObject(source)) {