Update mgol's name in AUTHORS, add .mailmap

[mgol]

In this way mgol's past contribution is mapped correctly.

[mgol]

Test failures don't seem related to this PR.

[dead-horse]

I think this AUTHORS list is generated from git log (https://github.com/koajs/koa/blob/master/package.json#L11)

[fl0w]

This list was generated using git log .... So even if this gets merged as requested it'll be a recurring issue whenever AUTHORS is updated.

koa/package.json

Line 11 in 841844e

"authors": "git log --format='%aN <%aE>' | sort -u > AUTHORS"

[mgol]

@fl0w The command you pasted respects .mailmap per https://git-scm.com/docs/pretty-formats:

%aN': author name (respecting .mailmap, see git-shortlog[1] or git-blame[1])

So this shouldn't be an issue (and I see it taken into account locally).

[fl0w]

Oh, today I learned. Then I'm +1 :)

[codecov]

Codecov Report

Merging #1100 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1100   +/-   ##
=======================================
  Coverage   99.73%   99.73%           
=======================================
  Files           5        5           
  Lines         371      371           
=======================================
  Hits          370      370           
  Misses          1        1

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