docs: Fix anchor link written in reference link syntax.
docs: Fix anchor link written in reference link syntax.

This has been broken since it was added in a rewrite in July 2019 in
c931e76cf2fa7511c756c9ef8846ea7fd1f7f0f6. An incomplete fix was
made a few days later in 871fd57f5e2bd1b286e0357a28131efba2b71407.

synicalsyntax/zulip,shubhamdhama/zulip,rht/zulip,zulip/zulip,zulip/zulip,zulip/zulip,showell/zulip,andersk/zulip,hackerkid/zulip,synicalsyntax/zulip,rht/zulip,brainwane/zulip,kou/zulip,eeshangarg/zulip,shubhamdhama/zulip,brainwane/zulip,punchagan/zulip,brainwane/zulip,punchagan/zulip,andersk/zulip,timabbott/zulip,showell/zulip,brainwane/zulip,hackerkid/zulip,kou/zulip,showell/zulip,andersk/zulip,zulip/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,rht/zulip,kou/zulip,rht/zulip,zulip/zulip,timabbott/zulip,eeshangarg/zulip,hackerkid/zulip,zulip/zulip,shubhamdhama/zulip,eeshangarg/zulip,andersk/zulip,brainwane/zulip,rht/zulip,synicalsyntax/zulip,shubhamdhama/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,showell/zulip,shubhamdhama/zulip,synicalsyntax/zulip,punchagan/zulip,kou/zulip,zulip/zulip,rht/zulip,brainwane/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,shubhamdhama/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,synicalsyntax/zulip,punchagan/zulip,shubhamdhama/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,eeshangarg/zulip,synicalsyntax/zulip,timabbott/zulip,kou/zulip,andersk/zulip,punchagan/zulip,kou/zulip,andersk/zulip,timabbott/zulip,showell/zulip,timabbott/zulip,eeshangarg/zulip,showell/zulip