Stork can 404 on losing access to a repo

[brendanmcfarland]

We saw 404's on stork today when:

• there had been a recent commit to to-fix-internal
• @rclark removed stork from to-fix-internal shortly after the commit

End result was

2017-10-30T20:40:44.102Z    99a31736-bdb2-11e7-8ec9-fd593e309025    { HTTPError: Response code 404 (Not Found)
at stream.catch.then.e (/var/task/node_modules/got/index.js:123:13)
at process._tickDomainCallback (internal/process/next_tick.js:135:7)
message: 'Response code 404 (Not Found)',
host: 'api.github.com',
hostname: 'api.github.com',
method: 'POST',
path: '/repos/mapbox/to-fix-internal/statuses/0eb154f84c9ed67ae8892dd754516cb69689ace2',
statusCode: 404,
statusMessage: 'Not Found' }

That gitsha exists, but stork couldn't see it any longer because it no longer had access to to-fix-internal

The errors subsided on its own after the initial trouble; posting this ticket to document another github api edge case where stork can run into trouble.

cc: @rclark