[ISSUE]Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed.

在使用 ng-repeat 的时候，遇到如上问题，解决办法

http://www.anujgakhar.com/2013/06/15/duplicates-in-a-repeater-are-not-allowed-in-angularjs/

ng-repeat = "item in items track by $index"