patch 8.1.1961: 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.  Add a test for
            mapcheck().
diff --git a/src/testdir/test70.in b/src/testdir/test70.in
index 9fbe818..9ee59c3 100644
--- a/src/testdir/test70.in
+++ b/src/testdir/test70.in
@@ -25,7 +25,7 @@
 :mz (vim-set-buff-line (vim-eval "line('.')") "1 changed line 1")
 :" scalar test
 :let tmp_string = mzeval('"string"')
-:let tmp_1000 = mzeval('1000')
+:let tmp_1000 = '1000'->mzeval()
 :if tmp_string . tmp_1000 == "string1000"
 :let scalar_res = "OK"
 :else