patch 9.0.1540: reverse() on string doesn't work in compiled function

Problem:    reverse() on string doesn't work in compiled function.
Solution:   Accept string in argument type check. (Yegappan Lakshmanan,
            closes #12377)
diff --git a/src/version.c b/src/version.c
index 5d55e4c..e5f4afa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1540,
+/**/
     1539,
 /**/
     1538,