trigger-rtd: fix role syntax

This doesn't need a name: when included like this.  I guess Ansible
accepts it, but it doesn't document this working anywhere.

Change-Id: Ibe6fa9296041af54f39a3ef69957d0e8a0df0259

playbooks/publish/trigger-rtd.yaml

@@ -1,3 +1,3 @@
 - hosts: localhost
   roles:
-    - name: trigger-readthedocs
+    - trigger-readthedocs