test(NavBar): update test cases

src/cell-group/test/__snapshots__/index.spec.js.snap

@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`should render title slot and match snapshot 1`] = `
+exports[`should render title slot correctly 1`] = `
 <div class="van-cell-group__title">Custom Title</div>
 <div class="van-cell-group van-hairline--top-bottom">
   <!---->

src/cell-group/test/index.spec.js

@@ -1,7 +1,7 @@
 import CellGroup from '..';
 import { mount } from '@vue/test-utils';
 
-test('should render title slot and match snapshot', () => {
+test('should render title slot correctly', () => {
   const wrapper = mount(CellGroup, {
     slots: {
       title: () => 'Custom Title',