Remove NW.js
Remove NW.js

Given that it's available in the normal repo, we no longer need it here.

https://github.com/caskroom/homebrew-cask/blob/master/Casks/nwjs.rb
noamross/homebrew-versions,elovelan/homebrew-versions,pquentin/homebrew-versions,lukaselmer/homebrew-versions,lukasbestle/homebrew-versions,coeligena/homebrew-verscustomized,tomschlick/homebrew-versions