Deprecation warnings in v0.10 and v11 nightlies

[cwebster2]

NeoVim Version
NVIM v0.11.0-dev-4+ga66424617

Describe the bug
Deprecation warning for vim.tbl_flatten

To Reproduce
Start nvim with nvim-nio enabled

vim.tbl_flatten is deprecated, use vim.iter(…):flatten():totable() instead. :help deprecated
Feature will be removed in Nvim 0.12
stack traceback:
        vim/shared.lua: in function 'tbl_flatten'
        ...casey/.local/share/nvim/lazy/nvim-nio/lua/nio/logger.lua:39: in function 'path_join'

nvim-nio/lua/nio/logger.lua

Line 39 in 8765cbc

return table.concat(vim.tbl_flatten({ ... }), path_sep)

[rcarriga]

Closed by #18