patch 8.1.1809: more functions can be used as a method

Problem:    More functions can be used as a method.
Solution:   Add has_key(), split(), str2list(), etc.
diff --git a/src/version.c b/src/version.c
index 80e0ce1..83c11ab 100644
--- a/src/version.c
+++ b/src/version.c
@@ -774,6 +774,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1809,
+/**/
     1808,
 /**/
     1807,