Sources are not correctly included in npm package

It seems that #1041 requested to include trix sources in NPM package, which was supposedly done by #1065. But it includes just the first level of sources, which does not seems to be really useful.

It does not cause any troubles to me except raised eyebrows 🤨

Review issues #1041 and #1065, then inspect the generated npm package to see which source files and nested directories are included. Done means the package contains the complete intended Trix sources rather than only the first level; the payload names no specific files or tests to run.

Written by the indexing model from the issue text.