settings: Fix the type annotation for color-hash

The (element-type) annotation cannot be used with properties that return
container types like GHashTable; we need to use the (type) annotation.

https://bugzilla.gnome.org/show_bug.cgi?id=750489

gtk/gtksettings.c

@@ -920,7 +920,7 @@ gtk_settings_class_init (GtkSettingsClass *class)
   g_assert (result == PROP_ERROR_BELL);
 
   /**
-   * GtkSettings:color-hash: (element-type utf8 Gdk.Color)
+   * GtkSettings:color-hash: (type GLib.HashTable(utf8,Gdk.Color)) (transfer container)
    *
    * Holds a hash table representation of the #GtkSettings:gtk-color-scheme
    * setting, mapping color names to #GdkColors.