neovim issues

Noticed an issue with a clean nvim setup when adding this plugin using vim-plug

```
Error detected while processing vim/plugged/vim-reasonml/plugin/console.vim:
line 31:
E121: Undefined variable: v:none
E116: Invalid arguments for function type
```

Seems to be an issue with this commit for backwards compatibility with vim:

https://github.com/jordwalke/vim-reasonml/commit/4b5bdcf0f191f51724f09a3b783d632691e914e5

```
:version
NVIM v0.9.1
Build type: Release
LuaJIT 2.1.0-beta3
```

Commenting out the polyfill lines seems to fix it

Start with plugin/console.vim around line 31 and compare it with commit 4b5bdcf0f191f51724f09a3b783d632691e914e5. Reproduce the error in a clean Neovim v0.9.1 setup using vim-plug, then verify that the compatibility handling no longer produces the reported errors and that the plugin loads successfully.

Written by the indexing model from the issue text.