Use new vim.validate() function

[nilscc]

Fixes #82

[h3xOo]

Sorry to tell you, but I've just found this:

[anthraxx]

This is now actively emitting warnings in neovim 0.12:

- ⚠️ WARNING vim.validate{<table>} is deprecated. Feature will be removed in Nvim 1.0
  - ADVICE:
    - use vim.validate(<params>) instead.
    - stack traceback:
        /home/anthraxx/.local/share/nvim/lazy/cmp-buffer/lua/cmp_buffer/source.lua:34
        /home/anthraxx/.local/share/nvim/lazy/cmp-buffer/lua/cmp_buffer/source.lua:45
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/source.lua:239
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/source.lua:283
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/core.lua:308
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/core.lua:178
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/core.lua:170
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/init.lua:372
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/utils/autocmd.lua:53
        /home/anthraxx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/utils/autocmd.lua:14

[nilscc]

I wonder why it was reverted...? 🤔