[fixed] JSSDemo

Summary: There was a typo fix sitting in my working copy that should be pushed upstream.

Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, #material_motion

Tags: #material_motion

Differential Revision: http://codereview.cc/D3450

packages/demos-react/src/JSSDemo.tsx

@@ -60,7 +60,7 @@ const getLayerClasses = ({ foreground$, background$ }) => {
   ).attach();
 
   return sheet.classes;
-})
+}
 
 const getLayerTranslateStreams = () => {
   const {