fix strftime %y for negative tm_year
diff --git a/src/time/strftime.c b/src/time/strftime.c
index f1ccc4d..e103e02 100644
--- a/src/time/strftime.c
+++ b/src/time/strftime.c
@@ -167,6 +167,7 @@
 		goto nl_strftime;
 	case 'y':
 		val = tm->tm_year % 100;
+		if (val<0) val += 100;
 		goto number;
 	case 'Y':
 		val = tm->tm_year + 1900LL;