doc: fix warning treated as an error

Typical error:

```
Warning, treated as error:
/home/jenkins-build/build/workspace/ceph-ansible-docs-pull-requests/docs/source/day-2/upgrade.rst:2:Title underline too short.
```

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 5c254861bdc146d3ef73dc99d6f52f7d03e22deb)

diff --git a/docs/source/day-2/upgrade.rst b/docs/source/day-2/upgrade.rst
index 6b82cbddcee00c512fd1ae45adfad6902d102e2d..47978321cd0d9d2bd3abc2243120842963fd8ebc 100644 (file)
--- a/docs/source/day-2/upgrade.rst
+++ b/docs/source/day-2/upgrade.rst
@@ -1,5 +1,5 @@
 Upgrading the ceph cluster
--------------------
+--------------------------
 
 ceph-ansible provides a playbook in ``infrastructure-playbooks`` for upgrading a Ceph cluster: ``rolling_update.yml``.