Bump minimum Ansible version to 1.6.3

Since we're using the alternatives module to add the redis binaries
to the path, Ansible 1.6+ is required.

However, there's an issue with versions up to 1.6.3 which causes
failures on Ubuntu 12.04 because it can't find the correct path
for `update-alternatives`.

See ansible/ansible#7470 for details.
Merge pull request #1 from DavidWittman/path-min-version-fix

Bump minimum Ansible version to 1.6.3