Fix typo in HACKING.rst
Fix typo in HACKING.rst

Futher=>Further

Change-Id: I94f2001cd2e0a432cce6d2da0e105f9a16f47837

hyakuhei/cleantox,zancas/hacking,zancas/hacking,hyakuhei/cleantox,openstack-dev/hacking,openstack-dev/hacking