Use our fork of react-gemini-scrollbar to fix resize issues

Rather than telling react-gemini-scrollbar to update every time something that
changes its size happens, try out our fork of it which uses some hackery to
listen for resizes.

src/components/structures/RoomView.js

@@ -1042,13 +1042,7 @@ module.exports = React.createClass({
     },
 
     onChildResize: function() {
-        // When the video, status bar, or the message composer resizes, the
-        // scroll panel also changes size.  Work around GeminiScrollBar fail by
-        // telling it about it. This also ensures that the scroll offset is
-        // updated.
-        if (this.refs.messagePanel) {
-            this.refs.messagePanel.onResize();
-        }
+        // no longer anything to do here
     },
 
     showSettings: function(show) {