[gtk+] gtk-demo: Add forgotten source file

[Matthias Clasen <matthiasc src gnome org>]

commit eab0df12a84e975c044e0b7966b9b9c2baf9411d
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jun 19 22:03:19 2015 -0400

    gtk-demo: Add forgotten source file
    
    The font_features.c file was not added as a resource, so that
    gtk3-demo could not display it.

 demos/gtk-demo/demo.gresource.xml |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/demos/gtk-demo/demo.gresource.xml b/demos/gtk-demo/demo.gresource.xml
index f05d86c..657442e 100644
--- a/demos/gtk-demo/demo.gresource.xml
+++ b/demos/gtk-demo/demo.gresource.xml
@@ -132,6 +132,7 @@
     <file>event_axes.c</file>
     <file>expander.c</file>
     <file>flowbox.c</file>
+    <file>font_features.c</file>
     <file>gestures.c</file>
     <file>glarea.c</file>
     <file>headerbar.c</file>