Merge branch 'add/ipv6' into 'master'

Add IPv6 support

See merge request !4

tasks/register-runner.yml

@@ -43,5 +43,6 @@
     --machine-machine-options 'digitalocean-region={{ gitlab_runner_digital_ocean_region }}'
     --machine-machine-options 'digitalocean-size={{ gitlab_runner_digital_ocean_size }}'
     --machine-machine-options 'digitalocean-private-networking'
+    --machine-machine-options 'digitalocean-ipv6'
   with_items: '{{ gitlab_runners }}'
   when: configured_runners.stderr.find('\n' + item.description) == -1