fix: remove ioutil from docs

docs/eventsub_docs.md

@@ -92,7 +92,7 @@ type eventSubNotification struct {
 }
 
 func eventsubFollow(w http.ResponseWriter, r *http.Request) {
-    body, err := ioutil.ReadAll(r.Body)
+    body, err := io.ReadAll(r.Body)
     if err != nil {
         log.Println(err)
         return