travis: ask travis to install python-yaml package.

If travis-ci has python-yaml package available, it will be able to parse
and check in details dabba yaml output.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
travis: remove useless comment.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
Merge pull request #15 from eroullit/travis-python-yaml

Travis python yaml support