[fix] travis: Permission denied: '/home/travis/.cache/pip/...'

Fix "Permission denied: '/home/travis/.cache/" errors from travis build [1].

Change owner https://docs.travis-ci.com/user/caching/#caches-and-read-permissions
and remove old log in the *before_caching* phase:

  https://docs.travis-ci.com/user/caching/#before_cache-phase

About pip cache see: https://docs.travis-ci.com/user/caching/#pip-cache



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

[1] https://travis-ci.org/github/asciimoo/searx/jobs/669664131#L220