Downgrade socket.io-client version

Author: CMEONE

package.json

@@ -16,7 +16,7 @@
     "idb": "^4.0.5",
     "register-service-worker": "^1.7.1",
     "semver": "^5.7.0",
-    "socket.io-client": "^4.4.1",
+    "socket.io-client": "^2.3.0",
     "vue": "^2.6.12",
     "vue-content-loader": "^0.2.3",
     "vue-router": "^3.4.3",