event-last-push styling fix

When viewing a fresh install of GitLab on a mobile device after a branch with a name of sufficient length, the broken styling can be seen as follows:

I modified the css for .event-last-push and .event-last-push-text to make it look correct:

As this is a purely css change, I don't believe it will break any tests. The only occurrence of .event-last-push* is in ./app/views/events/_event_last_push.html.haml