fix(errors): NavigationCanceled with async components

[lbwa]

Canceled behavior should always throw a same canceled error, instead of undefined

Same as these codes:

vue-router/src/history/base.js

Lines 160 to 162 in c8a4cef

	if (this.pending !== route) {
	return abort(createNavigationCancelledError(current, route))
	}

Related PR:

• Create router errors #3047

[posva]

Nice catch, thank you!
Can you remove the changes in the example folder and add a unit test instead like https://github.com/vuejs/vue-router/pull/3047/files#diff-c044368ddb9969465784dfa4ebfa75cd

[lbwa]

I will handle it soon

[lbwa]

@posva I have reverted redundant modifications and added extra unit test for PR

[posva]

Thanks!