i18n: fix global method in page-title guide

The change from i18n.t method to i18n.global.t for vue3 support was
missed in the page-title guide. I found this on the Intel router and am
pushing this for completeness.

Change-Id: I97c993e36caa07af6df7c1ae3124e4f9380c493b
Signed-off-by: Jason M. Bills <jason.m.bills@intel.com>

Author: jmbills

docs/guide/components/page-title/index.md

@@ -11,7 +11,7 @@ corresponds with the title property set in the route record's meta field in
     name: 'login',
     component: Login,
     meta: {
-      title: i18n.t('appPageTitle.login'),
+      title: i18n.global.t('appPageTitle.login'),
     },
   },
 ```