Change CSS class for message panel spinner

to stop scrollbars appearing when we
 - jump to a message or,
 - permalink that is to an not paginated in event

src/components/structures/TimelinePanel.js

@@ -1121,7 +1121,7 @@ var TimelinePanel = React.createClass({
         // exist.
         if (this.state.timelineLoading) {
             return (
-                    <div className={this.props.className + " mx_RoomView_messageListWrapper"}>
+                <div className="mx_RoomView_messagePanelSpinner">
                     <Loader />
                 </div>
             );