upgrade CodeMirror

bower.json

@@ -17,7 +17,7 @@
     "bootstrap": "http://getbootstrap.com/2.3.2/assets/bootstrap.zip",
     "jquery-tabby": "git://github.com/alanhogan/Tabby",
     "es5-shim": "~3.2.0",
-    "codemirror": "~3.20.0",
+    "codemirror": "~3.24.0",
     "showdown": "~0.3.1",
     "require-css": "~0.0.8"
   }