wrong assertion is used in the attachTo example (#1933)

geneowak · web-flow · commit f81292074ec4 · 2021-11-29T17:44:52.000+10:00
diff --git a/docs/api/options.md b/docs/api/options.md
@@ -317,13 +317,13 @@ const Component = {
 let wrapper = mount(Component, {
   attachTo: '#root'
 })
-expect(wrapper.vm.$el.parentNode).to.not.be.null
+expect(wrapper.vm.$el.parentNode).not.toBeNull()
 wrapper.destroy()
 
 wrapper = mount(Component, {
   attachTo: document.getElementById('root')
 })
-expect(wrapper.vm.$el.parentNode).to.not.be.null
+expect(wrapper.vm.$el.parentNode).not.toBeNull()
 wrapper.destroy()
 ```
 
