CI: add OSX/WIndows and node version to build matrix

Since we support multiple OSes it would be prudent to enable CI on a matrix of the OS and node versions supported. This would prevent OS and node version specific bugs which would be otherwise silently ignored.

Start by locating the repository's CI configuration and identifying which operating systems and Node.js versions the project supports. Add the supported OS and Node.js combinations to the build matrix, then verify that CI runs each combination and reports failures instead of silently omitting them.

Written by the indexing model from the issue text.