Flash of human un-friendly UTC timestamp for merge requests and issues

We should only render the timestamp value once it's been correctly formatted. I'm not sure if this is a ~bug or regression

It's a little hard to see in these gifs, because they're sped up. But sometimes the unformatted timestamp shows for several seconds.

2017-02-01_17.18.58

2017-02-01_17.18.03

2017-02-01_17.48.18

cc: @jschatz1