fix broken PREFIX_URL feature

ui/src/app/metube-socket.ts

@@ -0,0 +1,9 @@
+import { Injectable } from '@angular/core';
+import { Socket } from 'ngx-socket-io';
+
+@Injectable()
+export class MeTubeSocket extends Socket {
+     constructor() {
+        super({ url: '', options: {path: document.location.pathname + 'socket.io'} });
+    }
+}