Merge pull request #304 from yegor256/renovate/grunt-sass-4.x

Update dependency grunt-sass to v4

Author: yegor256

package.json

@@ -13,7 +13,7 @@
     "grunt": "^1.4.3",
     "grunt-contrib-watch": "1.1.0",
     "grunt-css-purge": "1.1.0",
-    "grunt-sass": "3.1.0",
+    "grunt-sass": "4.0.0",
     "grunt-sass-lint": "0.2.4",
     "load-grunt-tasks": "5.1.0",
     "node-sass": "9.0.0",