Fix vim.uv not existing

[the-moisrex]

User may not have uv installed either; this prevents that situation as well.

[lewis6991]

Users must have either vim.uv or vim.loop.

The README just provides and example. Users are generally expected to be running the latest release of Neovim which has vim.uv.

[the-moisrex]

I had to fix it on an almost fresh install of Ubuntu today; we either have to wait for OS package managers to catch up, or we could do this.

[lewis6991]

Use local uv = vim.uv or vim.loop then.

[the-moisrex]

@lewis6991 is it okay now?

[lewis6991]

Squash please.

[the-moisrex]

@lewis6991 done