Merge pull request #1203 from pi-hole/tweak/v5-v6-upgrade

WEBPASSWORD_FILE was added back in

Author: yubiuser

docs/docker/upgrading/v5-v6.md

@@ -90,4 +90,3 @@ The following variables can be removed without replacement, as they are no longe
 - `WEB_GID`
 - `WEB_UID`
 - `WEBLOGS_STDOUT`
-- `WEBPASSWORD_FILE`