Edit 3: Starting in version 0.4.0, ES6 syntax can be turned on by adding a jsconfig.json file to the project folder with the following contents:
jsconfig.json
This link helped a lot. Adding the jsconfig.json file to the the project didn't help much or rather it's not the best solution. Go to file > preferences > settings. In the settings.json file add this line:
"jshint.options": { "esversion": 6 }