fix: Update default Redirect URI port number (#152)

This PR resolves an issue where the default port number for Laravel (80)
doesn't match the default port number for the development server (8000),
which is what our quickstart guidance suggests using to get up and
running rapidly.

sample/.env.example

@@ -62,3 +62,4 @@ AUTH0_DOMAIN={DOMAIN}
 AUTH0_CLIENT_ID={CLIENT_ID}
 AUTH0_CLIENT_SECRET={CLIENT_SECRET}
 AUTH0_AUDIENCE={API_IDENTIFIER}
+AUTH0_REDIRECT_URI=${APP_URL}/callback