Don't use .npmignore - Use "files" in package.json.

[infacto]

Fixes #27

From (old package content):

seymour
|= .github
|  \= workflows
|     \- ci.yml
|= bin
|  |- seymour
|  \- seymour.cmd
|= src
|  \- seymour.js
|- .editorconfig
|- .eslintrc
|- CHANGELOG.md
|- CODE_OF_CONDUCT.md
|- LICENCE
|- package.json
\- README.md

To (new package content with this commit):

package
|= src
|  \- seymour.js
|= bin
|  |- seymour
|  \- seymour.cmd
|- CHANGELOG.md
|- LICENCE
|- package.json
\- README.md

[dpogue]

This project is pretty much a perfect example of "npmignore is hard to keep up-to-date and you shouldn't use it" 😅
Thanks for the pull request to fix that!

You should (if you want) also add your name to the contributors list in package.json.