Make sidebar specs compatible w/ BootstrapVue 2

spec/frontend/sidebar/components/assignees/assignee_avatar_link_spec.js

@@ -24,6 +24,7 @@ describe('AssigneeAvatarLink component', () => {
     };
 
     wrapper = shallowMount(AssigneeAvatarLink, {
+      attachToDocument: true,
       propsData,
       sync: false,
     });

spec/frontend/sidebar/components/assignees/collapsed_assignee_list_spec.js

@@ -16,6 +16,7 @@ describe('CollapsedAssigneeList component', () => {
     };
 
     wrapper = shallowMount(CollapsedAssigneeList, {
+      attachToDocument: true,
       propsData,
       sync: false,
     });

spec/frontend/sidebar/components/assignees/uncollapsed_assignee_list_spec.js

@@ -18,6 +18,7 @@ describe('UncollapsedAssigneeList component', () => {
     };
 
     wrapper = mount(UncollapsedAssigneeList, {
+      attachToDocument: true,
       sync: false,
       propsData,
     });