[css-transforms-2] Fix syntax error.

Author: dbaron

css-transforms-2/Overview.bs

@@ -50,7 +50,7 @@ spec: html; type: element; text: a;
 <script>
 window.MathJax = {
   tex: {
-    inlineMath: [['$', '$']]
+    inlineMath: [['$', '$']],
     displayMath: [['$$', '$$']]
   },
   svg: {