patch 8.1.1954: more functions can be used as a method

Problem:    More functions can be used as a method.
Solution:   Allow more functions to be used as a method.
diff --git a/src/testdir/test_utf8.vim b/src/testdir/test_utf8.vim
index ab1616a..9470855 100644
--- a/src/testdir/test_utf8.vim
+++ b/src/testdir/test_utf8.vim
@@ -77,7 +77,7 @@
   let s = "\u304b\u3099\u3044"
   let l = [0x304b, 0x3099, 0x3044]
   call assert_equal(l, str2list(s, 1))
-  call assert_equal(s, list2str(l, 1))
+  call assert_equal(s, l->list2str(1))
   if &enc ==# 'utf-8'
     call assert_equal(str2list(s), str2list(s, 1))
     call assert_equal(list2str(l), list2str(l, 1))