roles/nginx: Switch to nginx stable branch

Remove old mainline repo and add stable repo to get nginx 1.8.0.

See: http://nginx.org/en/CHANGES-1.8

Signed-off-by: Alan Orth <alan.orth@gmail.com>

roles/nginx/tasks/main.yml

@@ -4,7 +4,11 @@
   tags: nginx
 
 - name: Add nginx.org mainline repo
-  apt_repository: repo="deb http://nginx.org/packages/mainline/ubuntu/ {{ ansible_distribution_release }} nginx" state=present
+  apt_repository: repo="deb http://nginx.org/packages/mainline/ubuntu/ {{ ansible_distribution_release }} nginx" state=absent
+  tags: nginx
+
+- name: Add nginx.org stable repo
+  apt_repository: repo="deb http://nginx.org/packages/ubuntu/ {{ ansible_distribution_release }} nginx" state=present
   tags: nginx
 
 - name: Install nginx