add IE 11 to browserslist

Created by: adipasquale

blind fix attempt for https://trello.com/c/bR6ukPkS/890-reparer-closest-pour-ie-11-18

I could not manage to reproduce bug with closest through browserstack :/

It's very unclear which closest is generating this error as we don't have source maps connected on sentry. From looking at the code we only explicitly call the vanilla closest (not the jQuery one) at one point in the code : the motif form js (apart from the super admin interface). However the events on sentry are spread among the whole admin so it doesn't seem linked to that one.