Switch to Bootstrap 4

app/assets/javascripts/application.js

@@ -10,9 +10,10 @@
 // Read Sprockets README (https://github.com/sstephenson/sprockets#sprockets-directives) for details
 // about supported directives.
 //
-//= require jquery
-//= require jquery_ujs
 //= require turbolinks
+//= require jquery3
+//= require rails-ujs
+//= require popper
 //= require bootstrap-sprockets
 //= require codemirror/codemirror
 //= require codemirror/addon/display/placeholder