[vala/arnaudb/nullable-info-in-glib2] Add a nullable info in glib2 vapi.

[Arnaud B. <arnaudb src gnome org>]

commit e803c838bc71c6daa9a851075bd75f4379dff6a9
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Wed Sep 18 02:24:21 2019 +0200

    Add a nullable info in glib2 vapi.
    
    The g_date_time_new_from_iso8601()
    function can take a null TimeZone.

 vapi/glib-2.0.vapi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/vapi/glib-2.0.vapi b/vapi/glib-2.0.vapi
index b6ff0c2d7..27f0cef15 100644
--- a/vapi/glib-2.0.vapi
+++ b/vapi/glib-2.0.vapi
@@ -3003,7 +3003,7 @@ namespace GLib {
                public DateTime.now_local ();
                public DateTime.now_utc ();
                [Version (since = "2.56")]
-               public DateTime.from_iso8601 (string text, TimeZone default_tz);
+               public DateTime.from_iso8601 (string text, TimeZone? default_tz);
                public DateTime.from_unix_local (int64 t);
                public DateTime.from_unix_utc (int64 t);
                [Version (deprecated_since = "2.62")]