Adds south-1 region (#94)

Author: nunomaduro

src/Regions.php

@@ -32,6 +32,7 @@ public static function available()
             'eu-west-2'    => 'EU (London) (eu-west-2)',
             'eu-west-3'    => 'EU (Paris) (eu-west-3)',
             'eu-north-1'   => 'EU (Stockholm) (eu-north-1)',
+            'eu-south-1'   => 'EU (Milan) (eu-south-1)',
             'me-south-1'   => 'Middle East (Bahrain) (me-south-1)',
             'sa-east-1'    => 'South America (São Paulo) (sa-east-1)',
         ];