travis: install cmake3 from a ppa
travis: install cmake3 from a ppa

We need cmake 2.8.12 so install cmake3 from a ppa.

Signed-off-by: David Aguilar <9de348c050f7cd1ca590883733c4e531ce610bf4@gmail.com>

davvid/wildmatch,davvid/wildmatch,davvid/wildmatch