correct require() syntax

Author: johnjbarton

src/jupyter_contrib_nbextensions/nbextensions/python-markdown/main.js

@@ -20,13 +20,13 @@ define([
     "use strict";
 
     var marked = null;
-    requirejs('nbextensions/python-markdown/marked.min', 
+    requirejs(['nbextensions/python-markdown/marked.min'], 
         function(marked_local) {
             marked = marked_local.marked;
         }, 
         function(e_ignored) {
             // fall back to components for v<6.
-            requirejs('components/marked/lib/marked', 
+            requirejs(['components/marked/lib/marked'], 
                 function(marked_compat) {
                     marked = marked_compat;
                 },