Update setup.md
Update setup.md

Updated the URL from `http://help.exercism.io/getting-started-with-javascript.html` to `http://exercism.io/languages/javascript` since http://help.exercism.io/ has been deprecated.
marcCanipel/xjavascript,marcCanipel/xjavascript,cloudleo/xjavascript,exercism/xjavascript,cloudleo/xjavascript,exercism/xjavascript