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_arglist.vim b/src/testdir/test_arglist.vim
index daed3d4..c486b18 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -88,7 +88,7 @@
   argadd Xargadd
   call assert_equal(curbuf, bufnr('%'))
   call assert_equal('', bufname('%'))
-  call assert_equal(1, line('$'))
+  call assert_equal(1, '$'->line())
   rew
   call assert_notequal(curbuf, '%'->bufnr())
   call assert_equal('Xargadd', '%'->bufname())