chore(3p): Bump nixpkgs channels

Bumps both nixos-unstable and nixos-20.03 to today's versions, as per
status.nixos.org

Contains minor fixes to things that broke because of the update:

* tazjin/frog: hardware.u2f is a deprecated setting
* glittershark/system: modSha256 in Go modules is now vendorSha256
* glittershark/owothia: removed version constraint on relude

Change-Id: Ib3e9612b1b06ed547b90e4f8b0ffe5ed7fe0a5c4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1642
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/xanthous/src/Xanthous/Orphans.hs

@@ -304,16 +304,9 @@ instance forall t name. (NFData t, Monoid t, NFData name)
                  => NFData (Editor t name) where
   rnf ed = getName @_ @name ed `deepseq` getEditContents ed `deepseq` ()
 
-instance NFData StdGen where
-  -- StdGen's fields are bang-patterned so this is actually correct!
-  rnf sg = sg `seq` ()
-
 deriving via (ReadShowJSON StdGen) instance ToJSON StdGen
 deriving via (ReadShowJSON StdGen) instance FromJSON StdGen
 
-instance Function StdGen where
-  function = functionShow
-
 --------------------------------------------------------------------------------
 
 instance CoArbitrary a => CoArbitrary (NonNull a) where