If a window.CodeMirror instance is available, use it

src/js/easymde.js

@@ -1,5 +1,5 @@
 'use strict';
-var CodeMirror = require('codemirror');
+var CodeMirror = window.CodeMirror || require('codemirror');
 require('codemirror/addon/edit/continuelist.js');
 require('./codemirror/tablist');
 require('codemirror/addon/display/fullscreen.js');