patch 8.1.0257: no test for pathshorten()

Problem:    No test for pathshorten().
Solution:   Add a test. (Dominique Pelle, closes #3295)
diff --git a/src/version.c b/src/version.c
index 8e21e98..36376e9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    257,
+/**/
     256,
 /**/
     255,