fix docker-ce repo on CentOS

roles/docker/tasks/main.yml

@@ -13,10 +13,13 @@
     - name: Enable docker-ce repo (CentOS)
       yum_repository:
         name: docker-ce
+        enabled: yes
         description: Docker Community Edition
         baseurl: https://download.docker.com/linux/centos/$releasever/$basearch/stable
+        gpgkey: https://download.docker.com/linux/centos/gpg
+        gpgcheck: yes
 
-    - name: Install docker packages
+    - name: Install docker packages (CentOS)
       yum:
         name:
           - docker-ce