mailmap: Add mailmap entry for Jesscia McKellar.
mailmap: Add mailmap entry for Jesscia McKellar.

Give preference to the email mentioned in commits that
are associated to Jessica's GitHub account.

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