Upgrade stylelint to 4.x

Author: simonsmith

package.json

@@ -29,7 +29,7 @@
     "postcss-import": "^8.0.2",
     "postcss-reporter": "^1.3.0",
     "read-file-stdin": "0.2.0",
-    "stylelint": "^2.3.5"
+    "stylelint": "^4.2.0"
   },
   "devDependencies": {
     "chai": "^3.4.1",
@@ -41,7 +41,7 @@
     "sinon": "^1.17.2",
     "sinon-as-promised": "^4.0.0",
     "sinon-chai": "^2.8.0",
-    "stylelint-config-suitcss": "^1.0.0"
+    "stylelint-config-suitcss": "^3.0.0"
   },
   "scripts": {
     "test": "npm run lint && mocha --reporter spec --slow 400 --timeout 3000",