Updated travis.yml git depth 1
Updated travis.yml git depth 1

We don't do any git operation except include last commit name, so we only need last commit, that will make travis-ci test faster.
Chocobozzz/PeerTube,Green-Star/PeerTube,Chocobozzz/PeerTube,Green-Star/PeerTube,Green-Star/PeerTube,Chocobozzz/PeerTube,Green-Star/PeerTube,Chocobozzz/PeerTube