[nautilus] nautilus-file: use const for the date format

[Carlos Soriano Sánchez <csoriano src gnome org>]

commit 3ab964de6238c8a3cce2e040fb013c33cc0ad806
Author: Carlos Soriano <csoriano gnome org>
Date:   Wed Feb 18 10:04:41 2015 +0100

    nautilus-file: use const for the date format

 libnautilus-private/nautilus-file.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libnautilus-private/nautilus-file.c b/libnautilus-private/nautilus-file.c
index 564b9ac..26d1d41 100644
--- a/libnautilus-private/nautilus-file.c
+++ b/libnautilus-private/nautilus-file.c
@@ -4683,7 +4683,7 @@ nautilus_file_get_date_as_string (NautilusFile       *file,
        GDateTime *file_date, *now;
        gint days_ago;
        gboolean use_24;
-       gchar *format;
+       const gchar *format;
        gchar *result;
        gchar *result_with_ratio;