am-time-ago doesn't work

[essivision]

I get time like this:
$scope.created_at = "2016-10-29 08:12:43"
and then it use it in your directive like this:
<span am-time-ago="created_at"></span>

some times error me in console:

TypeError: Cannot read property 'utc' of undefined

[essivision]

My problem solved. angular-moment loaded before momentjs

Thanks