RSVPBot should only reply to actual commands, and not any message that begins with rsvp.

[zachallaun]

Originally opened by @kokeshii wtfcarlos/RSVPBot#41

[livviest]

I came here to document this as an issue after this happened to me. :)

I think the easiest fix would be to alter the prefix/keyword from rsvp to !rsvp or /rsvp a la Zulip slash commands.