patch 8.1.2100: :mksession is not sufficiently tested

Problem:    :mksession is not sufficiently tested.
Solution:   Add more test cases. (Yegappan Lakshmanan, closes #4993)
diff --git a/src/version.c b/src/version.c
index 28660ef..cca023d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2100,
+/**/
     2099,
 /**/
     2098,