[gnome-boxes] app-window: Mark missing string for translation

[Piotr Drąg <piotrdrag src gnome org>]

commit c8aa21f492af36217d87acb6086b7dffb5a2043d
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Mon Feb 5 17:17:53 2018 +0100

    app-window: Mark missing string for translation

 src/app-window.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/app-window.vala b/src/app-window.vala
index e2635d3d..fcb91e6a 100644
--- a/src/app-window.vala
+++ b/src/app-window.vala
@@ -313,7 +313,7 @@ public void show_properties () {
 
     public void show_send_file () {
         var dialog = new Gtk.FileChooserDialog (
-                "Select files to transfer", this, Gtk.FileChooserAction.OPEN,
+                _("Select files to transfer"), this, Gtk.FileChooserAction.OPEN,
                 _("_Cancel"),
                 Gtk.ResponseType.CANCEL,
                 _("_Open"),