Use Ansible's version_compare instead of doing math on strings

I'm surprised this worked all these years actually. Since Ansible
version 1.6 it has been possible to use the version_compare filter
instead of doing math logic on strings.

See: https://docs.ansible.com/ansible/playbooks_tests.html

roles/nginx/tasks/letsencrypt.yml

@@ -22,7 +22,7 @@
 # dependencies certbot checks for on its first run
 # taken from running certbot right after a clean Ubuntu 16.04 install
 - name: Install certbot dependencies (Ubuntu 16.04)
-  when: ansible_distribution == 'Ubuntu' and ansible_distribution_version == '16.04'
+  when: ansible_distribution == 'Ubuntu' and ansible_distribution_version | version_compare('16.04', '==')
   apt: name={{ item }} state=present update_cache=yes
   with_items:
     - augeas-doc

roles/nginx/templates/vhost.conf.j2

@@ -63,7 +63,7 @@ server {
         # See: https://httpoxy.org/
         fastcgi_param HTTP_PROXY "";
 
-        {% if ansible_distribution_version == '16.04' %}
+        {% if ansible_distribution_version | version_compare('16.04', '==') %}
         fastcgi_pass unix:/run/php/php7.0-fpm-{{ domain_name }}.sock;
         {% else %}
         fastcgi_pass unix:/var/run/php5-fpm-{{ domain_name }}.sock;