Switch to upstream jenkins role

Now that our

   https://github.com/geerlingguy/ansible-role-jenkins/pull/190

is merged. This unbreaks rollout with ansible 2.5.

requirements.yml

-# Use fork until https://github.com/agx/ansible-role-jenkins is merged
-- src: https://github.com/agx/ansible-role-jenkins
-  version: jenkins_home_symlink
-  name: geerlingguy.jenkins
+- src: geerlingguy.jenkins
+  version: 3.4.0
 
 - src: geerlingguy.certbot
   version: 3.0.0