docs: Update Freenode to OFTC

Change-Id: Idaae03612dd7feabd2cdc57e510947328524e98b

doc/source/contributor/contributing.rst

@@ -24,7 +24,7 @@ Communication
 Kolla Ansible shares communication channels with Kolla.
 
 IRC Channel
-    ``#openstack-kolla`` (`channel logs`_) on Freenode
+    ``#openstack-kolla`` (`channel logs`_) on `OFTC <http://oftc.net>`_
 
 Weekly Meetings
     On Wednesdays at 15:00 UTC in the IRC channel (`meetings logs`_)