[task/github-readme/travis] Fix Travis-Badge and link

PHPBB3-11968
Merge branch 'task/github-readme/travis' into develop-olympus

* task/github-readme/travis:
  [task/github-readme/travis] Fix Travis-Badge and link
[ticket/11920] Pin MariaDB repository to avoid conflicts with Ubuntu MySQL.

PHPBB3-11920
Merge remote-tracking branch 'bantu/ticket/11920' into develop-olympus

* bantu/ticket/11920:
  [ticket/11920] Pin MariaDB repository to avoid conflicts with Ubuntu MySQL.
[ticket/11970] Add set -x to Travis setup scripts.

Output is hidden by Travis by default and this will allow easier debugging.

PHPBB3-11970
[ticket/11970] Make apt-get less quiet.

PHPBB3-11970
Merge remote-tracking branch 'github-bantu/ticket/11970' into develop-olympus

* github-bantu/ticket/11970:
  [ticket/11970] Make apt-get less quiet.
  [ticket/11970] Add set -x to Travis setup scripts.