add PubSub

 import dotenv from "dotenv";
 dotenv.config();
-import { GraphQLServer } from "graphql-yoga";
+import { GraphQLServer, PubSub } from "graphql-yoga";
 import morgan from "morgan";
 import schema from "./schema";
 import "./passport";
@@ -8,9 +8,11 @@ import { authenticateJWT } from "./passport";
 
 const PORT = process.env.PORT;
 
+const pubsub = new PubSub();
+
 const server = new GraphQLServer({
   schema,
-  context: ({ request }) => ({ request }),
+  context: ({ request }) => ({ request, pubsub }),
 });
 
 server.express.use(morgan("dev"));