refactor: Rename alias bugdown_verion to markdown_version.
refactor: Rename alias bugdown_verion to markdown_version.

This commit is part of series of commits aimed at renaming bugdown to
markdown.

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