Fix jsduck publish errors (GERRIT_BRANCH -> ZUUL_BRANCH)

The $GERRIT_BRANCH env variable has been deprecated and removed
in the last upgrade. We were pushing to doc.wikimedia.org/project/
instead of doc.wikimedia.org/project/version/ causing existing
links to go 404.

Bug: 60137
Change-Id: I44d417e1e988aa628d2bd949d1c0c9bfaff7efb2