guix download and GitHub

[HiPhish]

Hello Guix developers,

I wanted to try to bring the Neovim package up to date, but I am having 
trouble using `guix download`:

    $ guix download  https://github.com/neovim/neovim/archive/v0.3.0.tar.gz
    
    Starting download of /tmp/guix-file.cmWnGA
    From https://github.com/neovim/neovim/archive/v0.3.0.tar.gz...
    X.509 certificate of 'github.com' could not be verified:
      signer-not-found
      invalid
    
    failed to download "/tmp/guix-file.cmWnGA" from "https://github.com/
neovim/neovim/archive/v0.3.0.tar.gz"
    guix download: error: https://github.com/neovim/neovim/archive/
v0.3.0.tar.gz: download failed

This is probably something on my end that needs to be set up, but I don't know 
what. I barely know anything about certification. If someone can point me in 
the right direction I would be grateful.