Fix ngRepeat to allow keys starting with $

Dear angular team,

This issue that this PR is addressing is very similar to https://github.com/angular/angular.js/issues/1463. ngRepeat Directive does not show object/map keys that begin with $. Plunker link http://plnkr.co/edit/0bzuZbzrVX9xLP7e6oHL?p=preview.

I have follow the same idea that was used in PR https://github.com/angular/angular.js/pull/6253.

Thanks for all the great work.