[Request] Add boardgame.io

[extend1994]

Library name: boardgame.io
Git repository url: https://github.com/google/boardgame.io
npm package name or url (if there is one): https://www.npmjs.com/package/boardgame.io
License (List them all if it's multiple): MIT
Homepage: http://boardgame.io

6,510 stars on 2018/07/26.
It's recommended to use npm auto-update to fetch files for a browser.
See homepage and doc to know which files you need to add to cdnjs.
Hint: Under dist.

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