This fixes a bug that exists in the package that the Notmuch logo doesn't show
up in notmuch-hello. I'll try and make a couple of other changes before opening
a pull request back to Guix to fix it.
When I was relying on my external package channel I ended up with a conflict
being unable to upgrade a personal package because an issue with a Guix package
was preventing me from upgrading Guix itself.
