[gbrainy] Widget.SizeRequest() was made obsolete in Gtk 3.0

[Jordi Mas <jmas src gnome org>]

commit d7f6bb5e75b15b41b1d9f08d6ff7e8588c7a7eb9
Author: Jordi Mas <jmas softcatala org>
Date:   Mon Jan 29 22:35:05 2018 +0100

    Widget.SizeRequest() was made obsolete in Gtk 3.0

 src/Clients/Classical/gbrainy.cs |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/src/Clients/Classical/gbrainy.cs b/src/Clients/Classical/gbrainy.cs
index e2ec43a..5262765 100644
--- a/src/Clients/Classical/gbrainy.cs
+++ b/src/Clients/Classical/gbrainy.cs
@@ -647,9 +647,9 @@ namespace gbrainy.Clients.Classical
                void OnActivateToolbar (object sender, System.EventArgs args)
                {
                        int width, height;
-                       Requisition requisition;
+                       Requisition minimum_size, natural_size;
 
-                       requisition = toolbar.SizeRequest ();
+                       toolbar.GetPreferredSize(out minimum_size, out natural_size);
                        app_window.GetSize (out width, out height);
                        toolbar.Visible = !toolbar.Visible;
 
@@ -663,7 +663,7 @@ namespace gbrainy.Clients.Classical
                                Preferences.Set <bool> (Preferences.ToolbarShowKey, toolbar.Visible);
                                Preferences.Save ();
                        }
-                       app_window.Resize (width, height - requisition.Height);
+                       app_window.Resize (width, height - natural_size.Height);
                }
 
                void OnVerticalToolbar (object sender, System.EventArgs args)