update markdown example

I noticed the Markdown Editor example had some bugs in it. First, the external JS pointed to a minified version of ripple on rawgithub that isn't in the current branch. Second, the view was being created with
```
var view = new View({
  data: {
    text: '# title'
  }
});
```
and it seemed like nesting the `text` under `data` was causing the markdown extension to fail. I unnested it and got it working again; was that the best solution?