Fix typo in ZUUL infra variable
Fix typo in ZUUL infra variable

.zuul.yaml has NEWREF, so fix typo in tools/build-all-rst.sh.

Change-Id: Iae8414fbc5c6f087e2deb887e8215706034d8e41

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals