docs: Fix link in 3.0 upgrade docs.
docs: Fix link in 3.0 upgrade docs.

Noticed by neiljp (Neil Pilgrim) <github@kepier.clara.net>.

punchagan/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,brainwane/zulip,andersk/zulip,brainwane/zulip,kou/zulip,kou/zulip,hackerkid/zulip,brainwane/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,brainwane/zulip,zulip/zulip,brainwane/zulip,andersk/zulip,showell/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,zulip/zulip,punchagan/zulip,kou/zulip,rht/zulip,kou/zulip,brainwane/zulip,andersk/zulip,showell/zulip,brainwane/zulip,kou/zulip,punchagan/zulip,andersk/zulip,zulip/zulip,andersk/zulip,rht/zulip,kou/zulip,showell/zulip,punchagan/zulip,kou/zulip,andersk/zulip,zulip/zulip,showell/zulip,hackerkid/zulip,showell/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,hackerkid/zulip,showell/zulip,andersk/zulip,rht/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip