updated for version 7.4.591

Problem:    test_listlbr_utf8 fails when the conceal feature is not available.
Solution:   Check for the conceal feature. (Kazunobu Kuriyama)

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    591,
 /**/
     590,
 /**/