Update vanillajs.md
Update vanillajs.md

Updated link using /libraries/lock#-show-options-callback-  https://github.com/auth0/docs/issues/565
sandrinodimattia/docs,khorne3/docs,Catografix/docs,hamzawi06/docs,miparnisari/docs,sandrinodimattia/docs,auth0/docs,Annyv2/docs,khorne3/docs,auth0/docs,khorne3/docs,hamzawi06/docs,jeffreylees/docs,yvonnewilson/docs,Catografix/docs,Catografix/docs,Annyv2/docs,sandrinodimattia/docs,jeffreylees/docs,yvonnewilson/docs,yvonnewilson/docs,hamzawi06/docs,Annyv2/docs,auth0/docs,jeffreylees/docs