fix config.root() so it returns a string or nil

[jonathannerat]

config.root() should return string?, but vim.loop.fs_realpath returns a 3-tuple (see :help vim.uv.fs_realpath and :help luv-error-handling). By adding parentheses around the function call, we force the function to return the first value of the tuple, which also fixes config.types() so it returns string? as well.

This fixes an error when trying to use rocks.nvim to install neodev.nvim. Since the types/ folder is nowhere to be found when installing neodev.nvim with luarocks, the call to fs_realpath returns an error, and stops the execution after any call to config.types() (which happens when trying to setup library folders for the LSP. This creates a bunch of Undefined global 'vim' appear on my init.lua config.

Although this looks like a fix specifically for my use case with rocks.nvim, it makes the function comply with it's signature, which I see as a good thing in the long run.

[jonathannerat]

Oops, my bad, I thought the signature for config.root() meant that it returned a string?, but it's actually for it's argument. Still, I think the fix should be considered, since luals.library() calls config.types(), which calls config.root(), and when root() returns the error mentioned before, the call to luals.library() suddenly stops without errors, and the Undefined global vim error appears.