fix tests not working

downgrade mongodb and mongoose-unique-validator

package.json

@@ -42,7 +42,7 @@
         "jsonwebtoken": "^8.5.1",
         "mongoose": "^6.0.13",
         "mongoose-findorcreate": "^3.0.0",
-        "mongoose-unique-validator": "^3.0.0",
+        "mongoose-unique-validator": "^2.0.3",
         "morgan": "^1.10.0",
         "passport": "^0.5.0",
         "passport-google-oauth": "^2.0.0",
@@ -61,7 +61,7 @@
         "eslint-plugin-prettier": "^4.0.0",
         "eslint-plugin-react": "^7.27.1",
         "jest": "^26.6.0",
-        "mongodb-memory-server": "^8",
+        "mongodb-memory-server": "^6",
         "nodemon": "^2.0.15",
         "prettier-eslint": "^13.0.0",
         "supertest": "^6.1.6"