Add retry to travis to fix build timeout.
Add retry to travis to fix build timeout.

See http://docs.travis-ci.com/user/build-timeouts/ for details.
binuri/Markus,arkon/Markus,finnergizer/Markus,MarkUsProject/Markus,benjaminvialle/Markus,melneubert/Markus,WilsonChiang/Markus,ealonas/Markus,benjaminvialle/Markus,finnergizer/Markus,wkwan/Markus,arkon/Markus,david-yz-liu/Markus,melneubert/Markus,david-yz-liu/Markus,MarkUsProject/Markus,melneubert/Markus,finnergizer/Markus,melneubert/Markus,binuri/Markus,david-yz-liu/Markus,wkwan/Markus,jeremygoh/Markus,reidka/Markus,WilsonChiang/Markus,reidka/Markus,ealonas/Markus,finnergizer/Markus,WilsonChiang/Markus,reidka/Markus,ealonas/Markus,david-yz-liu/Markus,david-yz-liu/Markus,wkwan/Markus,arkon/Markus,ealonas/Markus,finnergizer/Markus,melneubert/Markus,finnergizer/Markus,arkon/Markus,binuri/Markus,WilsonChiang/Markus,ealonas/Markus,benjaminvialle/Markus,binuri/Markus,reidka/Markus,wkwan/Markus,jeremygoh/Markus,WilsonChiang/Markus,binuri/Markus,jeremygoh/Markus,melneubert/Markus,jeremygoh/Markus,jeremygoh/Markus,MarkUsProject/Markus,finnergizer/Markus,reidka/Markus,finnergizer/Markus,david-yz-liu/Markus,ealonas/Markus,wkwan/Markus,reidka/Markus,jeremygoh/Markus,WilsonChiang/Markus,binuri/Markus,reidka/Markus,WilsonChiang/Markus,benjaminvialle/Markus,melneubert/Markus,melneubert/Markus,MarkUsProject/Markus,wkwan/Markus,MarkUsProject/Markus,binuri/Markus,wkwan/Markus,benjaminvialle/Markus,arkon/Markus,ealonas/Markus,david-yz-liu/Markus,MarkUsProject/Markus,benjaminvialle/Markus,reidka/Markus,jeremygoh/Markus,wkwan/Markus,arkon/Markus,finnergizer/Markus,WilsonChiang/Markus,jeremygoh/Markus,david-yz-liu/Markus,arkon/Markus,ealonas/Markus,benjaminvialle/Markus,melneubert/Markus,binuri/Markus,wkwan/Markus,ealonas/Markus,MarkUsProject/Markus,david-yz-liu/Markus,reidka/Markus,arkon/Markus,MarkUsProject/Markus,arkon/Markus,jeremygoh/Markus,WilsonChiang/Markus,binuri/Markus