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/undo.c b/src/undo.c
index 040ec54..ebf18da 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3124,8 +3124,13 @@
     }
     else
 #endif
-	vim_snprintf((char *)buf, buflen, _("%ld seconds ago"),
-						      (long)(vim_time() - tt));
+    {
+	long seconds = (long)(vim_time() - tt);
+
+	vim_snprintf((char *)buf, buflen,
+		NGETTEXT("%ld second ago", "%ld seconds ago", seconds),
+		seconds);
+    }
 }
 
 /*
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,