update drone.yml

drone.yml

 - name: prepare
   image: plugins/docker
   settings:
-    registry: repo.unino.de
-    insecure: true
+    registry: reg.unino.de
+    insecure: false
     #auth: authtoken
     username:
       from_secret: reg-user
     password:
       from_secret: reg-pass
-    repo: repo.unino.de/library/debian-devel
+    repo: reg.unino.de/library/debian-devel
     #mirror: registry.hub.docker.com/library/busybox
 
     dry_run: true