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_lua.vim b/src/testdir/test_lua.vim
index 65753dc..cb5b95d 100644
--- a/src/testdir/test_lua.vim
+++ b/src/testdir/test_lua.vim
@@ -36,7 +36,7 @@
 
   " lua.eval with a string
   lua v = vim.eval('"abc"')
-  call assert_equal('string', luaeval('vim.type(v)'))
+  call assert_equal('string', 'vim.type(v)'->luaeval())
   call assert_equal('abc', luaeval('v'))
 
   " lua.eval with a list