Add files array to package.json

[eemeli]

This way, only the right files are included in the published package. With .gitignore set up as it is, the dist/ folder is not getting included in the package, but all the dotfiles are.

[jaydenseric]

Can this please be reviewed/merged? Unnecessary stuff is being published and making its way into people's node_modules: https://unpkg.com/[email protected]