Update DocImpact notifier with new dest addr.
Update DocImpact notifier with new dest addr.

The openstack documentation team has a new mailing list in part to
accomodate the DocImpact notifier. Update the destination address in
the notify_doc_impact script to send mail to
openstack-docs@lists.openstack.org.

Change-Id: I041194298a18e5f710c6e3bd7221dee2099733e8

open-switch/infra_puppet-jenkins,open-switch/infra_puppet-jenkins