You have edited the wrong file, namely the newsfeed.js file. You should be editing the config.js file which resides is the MagicMirror/config folder. If so, you should revert all your changes to their original state and edit the config.js entry for the newsfeed module. It should look something like this. I tested your url for NOS Algemeen and it works fine with the module.
{ module: "newsfeed", position: "bottom_bar", // This can be any of the regions. Best results in center regions. config: { feeds: [ { title: "NOS Algemeen", url: "http://feeds.nos.nl/nosnieuwsalgemeen", }, { title: "BBC", url: "http://feeds.bbci.co.uk/news/video_and_audio/news_front_page/rss.xml?edition=uk", }, ] } },Screenshot
<img src=https://www.dropbox.com/s/4umt2lz4m75eg6j/newsfeed.png?raw=1 />