Update npmignore

[s1hofmann]

Short overview
Update npmignore to limit files included in package

Use case
Reduce bloat in published package.

Detailed description
Currently the published nut.js package include generated docs, some e2e tests and more.
Since all of this is not required for clients to use nut.js, the npmrc file should be updated to limit published content.

[sidorares]

you probably meant package.json and not npmrc @s1hofmann ?

[s1hofmann]

Ah, stupid me!
You're right, @sidorares, I'm not referring to npmrc, but the npmignore file.