vim-patch:8.1.0547: modeline test with keymap still fails

Problem:    Modeline test with keymap still fails.
Solution:   Check that the keymap feature is available for the failure assert.
3067a4dd0d

src/nvim/testdir/test_modeline.vim

@@ -87,5 +87,8 @@ func Test_modeline_syntax_fails()
 endfunc
 
 func Test_modeline_keymap_fails()
+  if !has('keymap')
+    return
+  endif
   call s:modeline_fails('keymap', 'keymap=evil$CMD')
 endfunc