Test against Node 16

* Replaced node-sass dependency that isn't compatible with Node 16
* Added Node 16 to CI matrix
* Fixes #1894

grunt/config/sass.js

@@ -1,9 +1,8 @@
-const sass = require('node-sass');
+const sass = require('sass');
 
 module.exports = {
   options: {
     implementation: sass,
-    outputStyle: 'compact',
     sourceComments: false
   },
   dist: {