CI: update Nix version

Author: aspiwack

.github/workflows/ci.yaml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 env:
   # Bump this number to invalidate the Github-actions cache
   cache-invalidation-key: 0
-  nixpkgs-url: https://github.com/NixOS/nixpkgs/archive/7f9be6a505a31f88499c5d20d11f98accf5ae6ba.tar.gz
+  nixpkgs-url: https://github.com/NixOS/nixpkgs/archive/5c019127ad2da9c081a71b9d9b9b48c9438a6a51.tar.gz
   nix-cmd: nix-shell --pure --arg withDevTools "false" --run
 
 jobs:
@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: cachix/install-nix-action@v15
+    - uses: cachix/install-nix-action@v30
       with:
         nix_path: "${{ env.nixpkgs-url }}"
     - uses: cachix/cachix-action@v15
@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: cachix/install-nix-action@v15
+    - uses: cachix/install-nix-action@v30
       with:
         nix_path: "${{ env.nixpkgs-url }}"
     - uses: cachix/cachix-action@v15