Setup NPM publish on tagging

[nschonni]

I haven't setup this up before, but it looks like it should be fairly straight forward https://docs.travis-ci.com/user/deployment/npm/

@XhmikosR have you done this on other repos?

[XhmikosR]

The only place I had to was in AppVeyor's website in a similar way.

https://github.com/appveyor/website/blob/master/appveyor.yml#L37

For other stuff I haven't had the need to.