[glib] GSeekable: Fix g_seekable_truncate invoker reference

[Rico Tzschichholz <ricotz src gnome org>]

commit df66b25301a6b5b2481375bbf246d4c69ded5e99
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sat Nov 4 20:05:37 2017 +0100

    GSeekable: Fix g_seekable_truncate invoker reference
    
    https://bugzilla.gnome.org/show_bug.cgi?id=573251

 gio/gseekable.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gio/gseekable.c b/gio/gseekable.c
index 5b44602..5237e7f 100644
--- a/gio/gseekable.c
+++ b/gio/gseekable.c
@@ -159,7 +159,7 @@ g_seekable_can_truncate (GSeekable *seekable)
 }
 
 /**
- * g_seekable_truncate:
+ * g_seekable_truncate: (virtual truncate_fn)
  * @seekable: a #GSeekable.
  * @offset: new length for @seekable, in bytes.
  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.