patch 8.1.2247: "make vimtags" does not work in runtime/doc

Problem:    "make vimtags" does not work in runtime/doc.
Solution:   Test existence with "which" instead of "test -x". (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 5089d7d..6289798 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2247,
+/**/
     2246,
 /**/
     2245,