Update jquery.tokeninput.js

After jQuery 1.9, the function jQuery(this).outerHeight() returns an object.
So, to use this script on 1.9+ jquery you need to change the function show_dropdown() and add a 'true' parameter in order to work properly.
```
function show_dropdown() {
    dropdown
           .css({
                position: "absolute",
                top: $(token_list).offset().top + $(token_list).outerHeight(true),
                left: $(token_list).offset().left,
                zindex: 999
            })
            .show();
}
```
Since this change will not affect previous jquery versions (tested with 1.7) it should be added to the dist.

Enjoy.