Fixed typo in extensions.rst
Fixed typo in extensions.rst

Removed repeated word package
adamkozuch/slick,Asamsig/slick,knoldus/slick-1,olivergg/slick,knoldus/slick-1,seebcioo/slick,xavier-fernandez/slick,nafg/slick,dvinokurov/slick,Radsaggi/slick,xavier-fernandez/slick,mustajarvi/slick,easel/slick,trevorsibanda/slick,jkutner/slick,lukasz-golebiewski/slick,nremond/slick,xavier-fernandez/slick,nremond/slick,bmclane/slick,dotta/slick,lukasz-golebiewski/slick,kwark/slick,InsideVault/slick,mustajarvi/slick,dotta/slick,adamkozuch/slick,nuodb/slick,marko-asplund/slick,seebcioo/slick,jkutner/slick,AtkinsChang/slick,AtkinsChang/slick,nmartynenko/slick,nremond/slick,InsideVault/slick,Radsaggi/slick,bmclane/slick,nmartynenko/slick,olivergg/slick,easel/slick