Fix default_cell_type option for notebook

IPython/html/static/notebook/js/notebook.js

@@ -175,9 +175,7 b' define(['
     Notebook.options_default = {
         // can be any cell type, or the special values of
         // 'above', 'below', or 'selected' to get the value from another cell.
-        Notebook: {
-            default_cell_type: 'code'
-        }
+        default_cell_type: 'code'
     };
 
     /**