Adding nodejs/releasers as maintainers

[Richard Lau]

Refs: nodejs/Release#557
Refs: #901 (comment)

Any objections to adding the release team (@nodejs/releasers) as maintainers of https://github.com/nodejs/cigtm?

[Rich Trott]

Do it!

[Richard Lau]

I've added @nodejs/releasers as maintainers of https://github.com/nodejs/cigtm.