[libhandy] view-switcher-title: Replace the deprecated (allow-none) by (nullable)

[Alexander Mikhaylenko <alexm src gnome org>]

commit 740d4da2ec2c01e36f6b5efe9d3603ec591c7137
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Jul 15 17:00:52 2020 +0200

    view-switcher-title: Replace the deprecated (allow-none) by (nullable)

 src/hdy-view-switcher-title.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/hdy-view-switcher-title.c b/src/hdy-view-switcher-title.c
index 567c32de..0b384f6e 100644
--- a/src/hdy-view-switcher-title.c
+++ b/src/hdy-view-switcher-title.c
@@ -528,7 +528,7 @@ hdy_view_switcher_title_get_title (HdyViewSwitcherTitle *self)
 /**
  * hdy_view_switcher_title_set_title:
  * @self: a #HdyViewSwitcherTitle
- * @title: (allow-none): a title, or %NULL
+ * @title: (nullable): a title, or %NULL
  *
  * Sets the title of @self. The title should give a user additional details. A
  * good title should not include the application name.
@@ -571,7 +571,7 @@ hdy_view_switcher_title_get_subtitle (HdyViewSwitcherTitle *self)
 /**
  * hdy_view_switcher_title_set_subtitle:
  * @self: a #HdyViewSwitcherTitle
- * @subtitle: (allow-none): a subtitle, or %NULL
+ * @subtitle: (nullable): a subtitle, or %NULL
  *
  * Sets the subtitle of @self. The subtitle should give a user additional
  * details.