Update .travis.yml
Update .travis.yml

* need newer cmake, gcc, and clang than standard travis vm comes with
* builds with clang now
trailofbits/mcsema,jcranmer/mcsema,chubbymaggie/mcsema,trailofbits/mcsema,chubbymaggie/mcsema,alessandrogario/mcsema,jcranmer/mcsema,trailofbits/mcsema,jcranmer/mcsema,trailofbits/mcsema,chubbymaggie/mcsema,alessandrogario/mcsema,alessandrogario/mcsema,alessandrogario/mcsema,jcranmer/mcsema,chubbymaggie/mcsema