Check in node_modules directory

[eaftan]

As recommended by the Actions docs.

Fixes #36

[lrstanley]

Seems like the better approach might be to use ncc, no? I see it's also mentioned in the Action documentation, and I see other heavily-used Actions also use it (build, commit single dist file, and use that as an entrypoint).

Adding ~900 files due to node_modules (and with npm updates, causing many more in the future), is bad practice in the node community. Curious why Actions suggests doing that.