Added fake composer_github_oauth to tests/playbook.yml for issue #19 reproduction

tests/playbook.yml

@@ -2,6 +2,8 @@
 
 - hosts: all
   sudo: true
+  vars:
+    composer_github_oauth: f03401aae1e276abb073f987c08a32410f462e73
   roles:
     - { role: common,                      tags: apt      }
     - { role: ../../ansible-role-composer, tags: composer }