fix: client/package.json & client/yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-TAR-15032660
- https://snyk.io/vuln/SNYK-JS-TAR-15127355

Author: snyk-bot

client/package.json

@@ -8,7 +8,7 @@
     "http-proxy-middleware": "^0.19.1",
     "react": "^16.8.6",
     "react-dom": "^16.8.6",
-    "react-scripts": "3.0.1"
+    "react-scripts": "4.0.0"
   },
   "scripts": {
     "start": "react-scripts start",