chore(3p): bump NixOS channels to 2021-03-25

OpenSSL released an update which fixes two severity high security
issues:

* https://mta.openssl.org/pipermail/openssl-announce/2021-March/000197.html
* https://mta.openssl.org/pipermail/openssl-announce/2021-March/000198.html

Update to the nixpkgs (currently still master) commits updating OpenSSL.

Other changes:

* Use GHC 8.8.4 for haskell-language-server as GHC 8.8.3 got removed
  from nixpkgs last friday.

Change-Id: Ic1b2f49284e78193a4330da4bb4b718a797f5ab1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2653
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/owothia/shell.nix

@@ -9,6 +9,6 @@ args@{ pkgs ? (import ../../../. {}).third_party, ... }:
   buildInputs = with pkgs.haskellPackages; [
     cabal-install
     hlint
-    pkgs.haskell-language-server.ghc883
+    pkgs.haskell-language-server.ghc884
   ];
 }

users/glittershark/xanthous/shell.nix

@@ -11,6 +11,6 @@
     ghc-prof-flamegraph
     hp2pretty
     hlint
-    pkgs.haskell-language-server.ghc883
+    pkgs.haskell-language-server.ghc884
   ];
 }