renovate: Add stylelint group

Author: massongit

.github/renovate.json

@@ -2,5 +2,11 @@
   "extends": [
     "config:base"
   ],
-  "rangeStrategy": "replace"
+  "rangeStrategy": "replace",
+  "packageRules": [
+    {
+      "groupName": "stylelint",
+      "matchPackageNames": ["stylelint", "stylelint-config-recommended"]
+    }
+  ]
 }