travis: disable clang for now
travis: disable clang for now

clang works for me (F21), and I have no interest in trying to figure
out what is up with the ancient version of Ubuntu Travis uses.  So,
until https://github.com/travis-ci/travis-ci/issues/2046 is resolved
(or I switch to Drone), clang gets ignored in CI.

Signed-off-by: Evan Nemerson <178b62e73cc3fab9e30bf27b2372c9ff92401915@nemerson.com>

jibsen/squash,quixdb/squash,wolut/squash,jibsen/squash,quixdb/squash,wolut/squash,quixdb/squash,Cloudef/squash,jibsen/squash,wolut/squash,Cloudef/squash,Cloudef/squash