Remove REACT_APP_BACKEND flag from start script and add Babel plugin.

Author: Blari

package.json

@@ -6,7 +6,7 @@
   "homepage": "./",
   "scripts": {
     "build": "cross-env REACT_APP_BACKEND=true NODE_ENV=production PUBLIC_URL='./' react-app-rewired --openssl-legacy-provider build",
-    "start": "cross-env REACT_APP_BACKEND=false react-app-rewired --openssl-legacy-provider start",
+    "start": "cross-env react-app-rewired --openssl-legacy-provider start",
     "dev": "cross-env react-app-rewired --openssl-legacy-provider start",
     "test": "react-app-rewired --openssl-legacy-provider test",
     "format": "prettier --write src/"
@@ -94,6 +94,7 @@
   },
   "devDependencies": {
     "@babel/helper-call-delegate": "^7.12.13",
+    "@babel/plugin-proposal-private-property-in-object": "^7.14.5",
     "@testing-library/jest-dom": "^5.17.0",
     "@testing-library/react": "^14.1.2",
     "@testing-library/user-event": "^14.5.1",