Fix live updates to reaction row buttons

This makes the reaction row buttons take the current count as prop as an easy
way of ensuring they always trigger an update when the count changes.

Fixes https://github.com/vector-im/riot-web/issues/9954

src/components/views/messages/ReactionsRow.js

@@ -116,6 +116,7 @@ export default class ReactionsRow extends React.PureComponent {
             return <ReactionsRowButton
                 key={content}
                 content={content}
+                count={count}
                 mxEvent={mxEvent}
                 reactionEvents={events}
                 myReactionEvent={myReactionEvent}