docs: change @on-event to @event

[Tchoupinax]

Hello,

I lost few times because my event did not work and I finally see that I was using @on-sort-change="onSortChange" (copied from the documentation) while I must use @sort-change="onSortChange" in Vue.js

I update each time @on- was found in the repo.

Thank you for your work! :) Cheers!