DOC: Update subscriptions.mdx with TypedEventTarget location. (#3373)

Author: dpnova

website/src/pages/docs/features/subscriptions.mdx

@@ -441,7 +441,7 @@ can use an external datastore for distributing the events across all server repl
 [`Redis Pub/Sub`](https://redis.io/topics/pubsub) or [`Kafka`](https://kafka.apache.org/).
 
 The minimal `EventTarget` implementation is described by the
-[`TypedEventTarget` interface](https://github.com/dotansimha/graphql-yoga/blob/master/packages/event-target/typed-event-target/src/typed-event-target.ts).
+[`TypedEventTarget` interface](https://github.com/dotansimha/graphql-yoga/blob/master/packages/event-target/typed-event-target/src/index.ts#L18).
 
 Yoga comes with an `EventTarget` implementation for
 [Redis Pub/Sub](https://redis.io/docs/manual/pubsub/).