fix: Fixes nix install by using correct pkg-configDepends config key (#1372)

* fix: Fixes nix install by using correct pkg-configDepends config key

As reported by Hrafn Blóðbók, nix updated references to pkgconfig in its
codebase to use the `pkg-config` spelling, this seems to break the
installation of Carp using nix.

See this PR: NixOS/nixpkgs@9bb3fcc

* ci: Uses 21.05 release of nix to be compatible with pkg-config changes

Author: TimDeve

.github/workflows/nixpkgs.yml

@@ -12,7 +12,7 @@ jobs:
         os: [ubuntu-latest]
     steps:
     - uses: actions/checkout@v2.3.4
-    - uses: cachix/install-nix-action@v15
+    - uses: cachix/install-nix-action@v16
       with:
-        nix_path: nixpkgs=channel:nixos-20.09
+        nix_path: nixpkgs=channel:nixos-21.05
     - run: nix-build

default.nix

@@ -11,7 +11,7 @@ let
         cabal-install clang gdb
         ormolu hlint flamegraph ghc-prof-flamegraph
       ] ++ lib.optionals stdenv.isLinux [ linuxPackages.perf tinycc zig ];
-      pkgconfigDepends = [ SDL2 SDL2_image SDL2_mixer SDL2_ttf glfw ];
+      pkg-configDepends = [ SDL2 SDL2_image SDL2_mixer SDL2_ttf glfw ];
       enableLibraryProfiling = profiling;
       enableExecutableProfiling = profiling;
       enableSharedLibraries = false;