Fixes mobiledoc sample & removes jQuery from usage

- simpleMobiledoc sample was missing a closing bracket
- switched from jQuery to document.querySelector

README.md

@@ -31,9 +31,9 @@ var simpleMobiledoc = {
     [1, "p", [
       [[], 0, "Welcome to Content-Kit"]
     ]]
-  ]
+  ]]
 };
-var element = $('#editor')[0];
+var element = document.querySelector('#editor');
 var options = { mobiledoc: simpleMobiledoc };
 var editor = new ContentKit.Editor(element, options);
 ```