patch 8.1.0401: can't get swap name of another buffer

Problem:    Can't get swap name of another buffer.
Solution:   Add swapname(). (Ozaki Kiichi, closes #3441)
diff --git a/src/version.c b/src/version.c
index d3cc195..8195858 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    401,
+/**/
     400,
 /**/
     399,