zephyr_mirror.py: update zulip server url for zephyr documentation
zulipchat.com hosts the documentation (as well as the server); make the
url reflect it
@@ -86,7 +86,7 @@ while backoff.keep_going():
error_message = """
ERROR: The Zephyr mirroring bot is unable to continue mirroring Zephyrs.
This is often caused by failing to maintain unexpired Kerberos tickets
-or AFS tokens. See https://zulip.com/zephyr for documentation on how to
+or AFS tokens. See https://zulipchat.com/zephyr for documentation on how to
maintain unexpired Kerberos tickets and AFS tokens.
"""
print(error_message)
