patch 8.1.2038: has('vimscript-4') is always 0

Problem:    has('vimscript-4') is always 0.
Solution:   Add "vimscript-4" to the feature table. (Naruhiko Nishino,
            closes #4941)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 6772692..b352ea9 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3771,6 +3771,7 @@
 	"vimscript-1",
 	"vimscript-2",
 	"vimscript-3",
+	"vimscript-4",
 	"virtualedit",
 	"visual",
 	"visualextra",