[shotwell] Mark missing strings for translation

[Piotr Drąg <piotrdrag src gnome org>]

commit f0cc8ab7929242faa58f6aa69b7a123bec692f09
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Thu Sep 28 14:21:27 2017 +0200

    Mark missing strings for translation
    
    Unfortunately, Glade suffers from
    https://bugzilla.gnome.org/show_bug.cgi?id=782753

 ui/preferences_dialog.ui |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/ui/preferences_dialog.ui b/ui/preferences_dialog.ui
index abeda8e..60df1c2 100644
--- a/ui/preferences_dialog.ui
+++ b/ui/preferences_dialog.ui
@@ -665,7 +665,7 @@
       <object class="GtkHeaderBar" id="headerbar">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
-        <property name="title">Shotwell Preferences</property>
+        <property name="title" translatable="yes">Shotwell Preferences</property>
         <property name="show_close_button">True</property>
       </object>
     </child>