mailmap: Add mailmap entry for Reid Barton.
mailmap: Add mailmap entry for Reid Barton.

This is the email mentioned in commits that
are linked to Reid's GitHub account.

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