Update Datatables.php

Theres an error when using the search with characters like ā, ē, č, ū, š, etc...
It is because the code uses strtolower instead of mb_strtolower...

It is easily fixed by replacing strtolower function with \Str::lower for example.

See this Issue.. 
https://github.com/bllim/laravel4-datatables-package/issues/167