fix: Use correct welcome stream name (#104)

I thought that the current batches channel name was just the text, but
it really does include the emoji!

I found this out because Zulip messaged me this when PB tried to check
in today:

> Your bot '[email protected]' tried to send a message
to channel #**current batches**, but that channel does not exist. Click
[here]() to create it.

main.go

@@ -48,7 +48,7 @@ func main() {
 
 	projectId := "pairing-bot-284823"
 	botUsername := "[email protected]"
-	welcomeStream := "current batches"
+	welcomeStream := "🧑‍💻 current batches" // The emoji is literally part of the channel name!
 
 	log.Printf("Running the app in environment = %s", appEnv)