Gitlab CB v6.4.0

  * Bump gitlab-shell to v1.8.0
  * Bump gitlab to 6.4.0
  * Remove stale nginx config file
  * Default recipe changes
    - Update gitlab-shell config to point at /usr/local/bin/redis-cli
    - Fix permissions on .ssh/authorized_keys
    - Add rack_attack file
    - Add precompile assets execute
    - Add logrotate dependency and configuration