use sortable instead of sortEnabled - fix #1216

I supose `sortable` is the right flag here and `sortEnabled` has the same function.
`sortEnabled` is not used anywhere else in More source or specs, as far as I can see/search. 

This proposed change was [tested in my karma branch](https://travis-ci.org/SergioCrisostomo/mootools-more/builds/22829467) and got green

This is a fix for #1216