fix destroySlick() with new syntax
fix destroySlick() with new syntax

the new function-syntax was introduced with slick-carousel 1.4, and destroySlick() wasn't updated since
guillaumeduchemin/angular-slick,mykwillis/angular-slick,sherodtaylor/angular-slick,CapeSepias/angular-slick,jacob-meacham/angular-slick,BetaWaveLLC/angular-slick,vasyabigi/angular-slick,arinet/angular-slick,OdenFrey/angular-slick,guillaumeduchemin/angular-slick,stoneyb/angular-slick,CapeSepias/angular-slick,jacob-meacham/angular-slick,indiegogo/angular-slick,sherodtaylor/angular-slick,palgit/angular-slick,stoneyb/angular-slick,arinet/angular-slick,indiegogo/angular-slick,sky-uk/angular-slick,sky-uk/angular-slick,palgit/angular-slick,BetaWaveLLC/angular-slick,vasyabigi/angular-slick,OdenFrey/angular-slick,mykwillis/angular-slick