Update EasyPostServiceDescriptions.php

Closes #3480663

src/Service/EasyPostServiceDescriptions.php

@@ -152,7 +152,7 @@ class EasyPostServiceDescriptions {
         '3DaySelect' => $this->t('UPS Three-Day Select'),
       ],
       'USPS' => [
-        'First' => $this->t('USPS First Class'),
+        'GroundAdvantage' => $this->t('USPS Ground Advantage'),
         'Priority' => $this->t('USPS Priority'),
         'Express' => $this->t('USPS Express'),
         'ParcelSelect' => $this->t('USPS Parcel Select'),