fix wait_for_vue_resource to not rely on global Vue object

app/assets/javascripts/vue_shared/vue_resource_interceptor.js

-/* eslint-disable no-param-reassign, no-plusplus */
 import Vue from 'vue';
 import VueResource from 'vue-resource';
 
 Vue.use(VueResource);
 
+// Maintain a global counter for active requests
+// see: spec/support/wait_for_vue_resource.rb
 Vue.http.interceptors.push((request, next) => {
-  Vue.activeResources = Vue.activeResources ? Vue.activeResources + 1 : 1;
+  window.activeVueResources = window.activeVueResources || 0;
+  window.activeVueResources += 1;
 
   next(() => {
-    Vue.activeResources--;
+    window.activeVueResources -= 1;
   });
 });
 
+// Inject CSRF token so we don't break any tests.
 Vue.http.interceptors.push((request, next) => {
-  // needed in order to not break the tests.
   if ($.rails) {
+    // eslint-disable-next-line no-param-reassign
     request.headers['X-CSRF-Token'] = $.rails.csrfToken();
   }
   next();

spec/support/wait_for_vue_resource.rb

 module WaitForVueResource
   def wait_for_vue_resource(spinner: true)
     Timeout.timeout(Capybara.default_max_wait_time) do
-      loop until page.evaluate_script('Vue.activeResources').zero?
+      loop until page.evaluate_script('window.activeVueResources').zero?
     end
   end
 end