Minor documentation tweak to UPGRADE.md (#1526)

* Update UPGRADE.md

I just went through the steps of upgrading passport from v8 to v10 and hit a minor snag that could have been solved by a tweak to the documentation.
When upgrading from v8 to v9 it says place two Passport static calls "within the `boot` method of your `AppServiceProvider`"
When upgrading from v9 to v10 it says you can remove the calls from your `AuthServiceProvider`.

I don't claim to know where those calls belonged in the first place, so this proposal just updates the documentation to list them both.

* Update UPGRADE.md

Co-authored-by: Taylor Otwell <[email protected]>

Author: jonrmitchell

UPGRADE.md

@@ -16,7 +16,7 @@ Laravel 8.0 is now the minimum required version.
 
 PR: https://github.com/laravel/passport/pull/1325
 
-The personal client configuration methods have been removed from the `Passport` class since they are no longer necessary. You should remove calls to these methods from your `AuthServiceProvider`.
+The personal client configuration methods have been removed from the `Passport` class since they are no longer necessary. You should remove any calls to these methods from your application's service providers.
 
 ## Upgrading To 9.0 From 8.x