Call handleUnmount before rendering a new page (#1020)

Author: jkbailey

react_ujs/src/events/turbolinks.js

@@ -2,11 +2,11 @@ module.exports = {
   // Turbolinks 5+ got rid of named events (?!)
   setup: function(ujs) {
   	ujs.handleEvent('turbolinks:load', ujs.handleMount);
-    ujs.handleEvent('turbolinks:before-render', ujs.handleMount);
+    ujs.handleEvent('turbolinks:before-render', ujs.handleUnmount);
   },
 
   teardown: function(ujs) {
   	ujs.removeEvent('turbolinks:load', ujs.handleMount);
-    ujs.removeEvent('turbolinks:before-render', ujs.handleMount);
+    ujs.removeEvent('turbolinks:before-render', ujs.handleUnmount);
   },
 }