patch 8.1.0308: a quick undo shows "1 seconds ago"

Problem:    A quick undo shows "1 seconds ago". (Tony Mechelynck)
Solution:   Add singular/plural message.
diff --git a/src/version.c b/src/version.c
index bad2b33..51ead8f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    308,
+/**/
     307,
 /**/
     306,