Replace git.openstack.org URLs with opendev.org URLs

Change-Id: I3bd3bcffe335a3d93868c541181812a99b602c00
diff --git a/HACKING.rst b/HACKING.rst
index cd3c49c..3392185 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -1,4 +1,4 @@
 openstack Style Commandments
-===============================================
+============================
 
 Read the OpenStack Style Commandments https://docs.openstack.org/hacking/latest/