Add @babel/plugin-proposal-class-properties to devDependencies

Author: alex-christiansen

vanilla/counter/package.json

@@ -23,6 +23,7 @@
   "devDependencies": {
     "@babel/cli": "7.17.6",
     "@babel/core": "7.22.1",
+    "@babel/plugin-proposal-class-properties": "^7.18.6",
     "@babel/plugin-proposal-object-rest-spread": "^7.12.1",
     "@babel/plugin-transform-runtime": "7.22.4",
     "@babel/preset-env": "7.22.4",