Horizon docs have HAProxy headings

Thanks to evrardjp for calling this one out!

Closes-Bug: 1502122

Change-Id: I2b78e1006aec15f565f9aebd9972cd4fddb62ed7

doc/source/install-guide/configure-horizon.rst

@@ -1,12 +1,12 @@
 `Home <index.html>`__ OpenStack Ansible Installation Guide
 
-Configuring HAProxy (optional)
+Configuring Horizon (optional)
 ------------------------------
 
 Customizing the Horizon deployment is done within
 ``/etc/openstack_deploy/user_variables.yml``.
 
-Securing HAProxy communication with SSL certificates
+Securing Horizon communication with SSL certificates
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 The openstack-ansible project provides the ability to secure Horizon