Minified file preamble incorrect and not being added

Uglify is supposed to be adding something like:

```js
/* commonmark 1.2.3 https://github.com/jgm/CommonMark @license BSD3 */
```

to [`dist/commonmark.min.js` ](https://github.com/commonmark/commonmark.js/blob/fe6ce5a3d266ae3e320bb2329967f6368c690335/dist/commonmark.min.js) but it does not.

Also, shouldn't it link to this repo and not jgm/CommonMark?