Now using apt.postgresql.org for all Debians.

tasks/main.yml:
- Includes tasks/debian.yml if ansible_os_family is Debian, in
  order to always use apt.postgresql.org for Debians.

tasks/ubuntu.yml:
- No longer used, removed.
Merge pull request #5 from mtpereira/fix_ubuntu_repo

Now using apt.postgresql.org for all Debians.