Update stylelint config

…with updated plugins.

I have also specified that we will use string import notation, as url notation was causing errors.

.stylelintrc.json

@@ -1,3 +1,4 @@
 {
-  "extends": ["stylelint-config-standard-scss", "stylelint-config-prettier"]
+  "extends": ["stylelint-config-standard-scss", "stylelint-config-standard"],
+  "rules": { "import-notation": "string" }
 }