use 'npx relative-deps' instead of 'yarn relative-deps'

[faassen]

In a non-yarn NPM environment 'yarn relative-deps' obviously doesn't work, but 'npm run relative-deps' also doesn't work, which makes sense as there's no script. But the 'npx relative-command' does work so I propose we put this in instead.

[mweststrate]

Good points. Thanks!