use only valid sort directions
use only valid sort directions

fixes #9

ogizanagi/EasyAdminBundle,javiereguiluz/EasyAdminBundle,OskarStark/EasyAdminBundle,OskarStark/EasyAdminBundle,javiereguiluz/EasyAdminBundle,datagit/EasyAdminBundle,ogizanagi/EasyAdminBundle,thomasbeaujean/EasyAdminBundle,helios-ag/EasyAdminBundle,yceruto/EasyAdminBundle,peterkokot/EasyAdminBundle,gabiudrescu/EasyAdminBundle,alexgt9/EasyAdminBundle,npotier/EasyAdminBundle,jverdeyen/EasyAdminBundle,datagit/EasyAdminBundle,OskarStark/EasyAdminBundle,yceruto/EasyAdminBundle,kamilZ/EasyAdminBundle,datagit/EasyAdminBundle,kamilZ/EasyAdminBundle,Seanmcn/EasyAdminBundle,alexgt9/EasyAdminBundle,gabiudrescu/EasyAdminBundle,npotier/EasyAdminBundle,ogizanagi/EasyAdminBundle,alexgt9/EasyAdminBundle,kamilZ/EasyAdminBundle,thomasbeaujean/EasyAdminBundle,yceruto/EasyAdminBundle,seydu/EasyAdminBundle,gabiudrescu/EasyAdminBundle,seydu/EasyAdminBundle,seydu/EasyAdminBundle,ogizanagi/EasyAdminBundle,thomasbeaujean/EasyAdminBundle