fix useWebSocketImplementation so it works with pool on nodejs esm.

relay.ts

@@ -1,3 +1,5 @@
+/* global WebSocket */
+
 import { verifyEvent } from './pure.ts'
 import { AbstractRelay } from './abstract-relay.ts'
 
@@ -8,9 +10,19 @@ export function relayConnect(url: string): Promise<Relay> {
   return Relay.connect(url)
 }
 
+var _WebSocket: typeof WebSocket
+
+try {
+  _WebSocket = WebSocket
+} catch {}
+
+export function useWebSocketImplementation(websocketImplementation: any) {
+  _WebSocket = websocketImplementation
+}
+
 export class Relay extends AbstractRelay {
   constructor(url: string) {
-    super(url, { verifyEvent })
+    super(url, { verifyEvent, websocketImplementation: _WebSocket })
   }
 
   static async connect(url: string): Promise<Relay> {