specs: wait for ajax requests completion where required

spec/features/users/dossier_creation_spec.rb

@@ -78,6 +78,8 @@ feature 'As a User I wanna create a dossier' do
 
       page.find_by_id('dossier-siret').set siret
       page.find_by_id('submit-siret').click
+      wait_for_ajax
+
       expect(page).to have_css('#recap-info-entreprise')
       find(:css, "#dossier_autorisation_donnees[value='1']").set(true)
       page.find_by_id('etape_suivante').click