patch 8.1.2157: libvterm source files missing from distribution

Problem:    Libvterm source files missing from distribution.
Solution:   Rename source files. (closes #5065)
diff --git a/src/version.c b/src/version.c
index 573b5cc..f8602f7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2157,
+/**/
     2156,
 /**/
     2155,