README: flakes don't need the special installer anymore

Fix #114

Author: domenkozar

README.md

@@ -55,8 +55,6 @@ jobs:
     - uses: actions/[email protected]
     - uses: cachix/install-nix-action@v15
       with:
-        install_url: https://nixos-nix-install-tests.cachix.org/serve/vij683ly7sl95nnhb67bdjjfabclr85m/install
-        install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
         extra_nix_config: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
     - run: nix build