fix undefind vim in lua lsp

[Nicals]

Reverts #5 and use nvim_workspace.

Source: https://github.com/VonHeikemen/lsp-zero.nvim/blob/main/advance-usage.md

[startwarfields]

thanks! this fixed the issue for me. sumneko_lua also no longer seems to be available

note: I had to save, source, and reload nvim for the lsp to propagate.