rocketchat: fix reactToMessages callback

rocketchat is dumb and sends an array of one message since version 3.8.0.
see RocketChat/Rocket.Chat#20801
this is scheduled to be fixed in version 3.12.0

index.js

@@ -77,7 +77,8 @@ function RocketChat (skyfall) {
           source: id,
         });
 
-        return driver.reactToMessages((error, message) => {
+        return driver.reactToMessages((error, messages) => {
+          message = messages[0]
           if (error) {
             skyfall.events.emit({
               type: `rocketchat:${ name }:error`,