[gnome-robots] Use Unicode quotation marks in a user-visible string

[Piotr Drąg <piotrdrag src gnome org>]

commit f95dac7d1f587ddc133b1aa4068c596790eaa80e
Author: Piotr Drąg <piotrdrag gmail com>
Date:   Wed Feb 6 20:32:30 2019 +0100

    Use Unicode quotation marks in a user-visible string
    
    See https://developer.gnome.org/hig/stable/typography.html

 src/graphics.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/graphics.c b/src/graphics.c
index 846b3a9..b35b0d6 100644
--- a/src/graphics.c
+++ b/src/graphics.c
@@ -146,7 +146,7 @@ load_bubble_graphic (gchar * fname, GdkPixbuf ** pixbuf)
 {
 
   if (!g_file_test (fname, G_FILE_TEST_EXISTS)) {
-    printf (_("Could not find \'%s\' pixmap file\n"), fname);
+    printf (_("Could not find “%s” pixmap file\n"), fname);
     return FALSE;
   }