Update stylelint to use peerDependencies instead of devDependencies

Author: ntwb

packages/stylelint-config/package.json

@@ -29,7 +29,7 @@
 	"dependencies": {
 		"stylelint-config-wordpress": "^16.0.0"
 	},
-	"devDependencies": {
+	"peerDependencies": {
 		"stylelint": "^12.0.0"
 	},
 	"publishConfig": {