fix docker repo tag

roles/docker/tasks/main.yml

@@ -16,7 +16,7 @@
 
 - name: Add docker deb repository
   apt_repository:
-    repo: "deb http://apt.dockerproject.org/repo {{ ansible_distribution_release }} main"
+    repo: "deb http://apt.dockerproject.org/repo ubuntu-{{ ansible_distribution_release }} main"
     state: present
   tags:
     - docker