Fix sniff warning about underlying being too short.

Author: GaneshChandrasekaran-zz

components/lock.rst

@@ -517,7 +517,7 @@ can be two running containers in parallel.
     on the old one.
 
 ZookeeperStore
-~~~~~~~~~~
+~~~~~~~~~~~~~~
 
 The way ZookeeperStore works is by maintaining locks in ephemeral nodes within ``PHP_LOCK_NODE`` on the server. That means that by using
 the :ref:`ZookeeperStore <lock-store-zookeeper>` the locks will be automatically released at the end of the session