[libgit2-glib] fix GgitDiffLineCallback signature

[Alberto Fanjul <albfan src gnome org>]

commit 5d4baea50249d88c25db48dc735b24b16bd2199a
Author: Alan Knowles <alan roojs com>
Date:   Thu Mar 14 14:42:34 2019 +0800

    fix GgitDiffLineCallback signature

 libgit2-glib/ggit-types.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/libgit2-glib/ggit-types.h b/libgit2-glib/ggit-types.h
index b6d91c3..4d5accf 100644
--- a/libgit2-glib/ggit-types.h
+++ b/libgit2-glib/ggit-types.h
@@ -1140,7 +1140,7 @@ typedef gint (* GgitDiffHunkCallback) (GgitDiffDelta *delta,
 /**
  * GgitDiffLineCallback:
  * @delta: a #GgitDiffDelta.
- * @hunk: a #GgitDiffHunk.
+ * @hunk: (nullable): a #GgitDiffHunk.
  * @line: a #GgitDiffLine.
  * @user_data: (closure): user-supplied data.
  *