Small range raises stack overflow

Changing the readme example to:

``` javascript
var Tree = require('interval-tree');
var itree = new Tree(300);
itree.add([22, 43, 'foo']);
```

Will raise a `Maximum call stack size exceeded` in `SortedList.js:26:17`.
Is there something wrong with this code?

_ps. interval-tree@0.1.0_
