Fixed artifacts expire date in FF

## What does this MR do?

FireFox was trying to parse the date incorrectly so it would just show 'Past due'

## Screenshots (if relevant)

![Screen_Shot_2016-07-21_at_17.16.57](/uploads/938d39c648dc98540cd991cf552276dd/Screen_Shot_2016-07-21_at_17.16.57.png)

See merge request !5403