Update to haskell.nix with pkg-config fix

This will include the patch that was added in
input-output-hk/haskell.nix#874
to fix this issue:

```
Setup: The program 'pkg-config' version >=0.9.0 is required but it could not
be found.

builder for '/nix/store/16bf6j2f1fig368pi1yfv70x5njs8d6y-cardano-crypto-class-lib-cardano-crypto-class-2.0.0-x86_64-w64-mingw32.drv' failed with exit code 1
```

Author: mrBliss

nix/sources.json

@@ -5,10 +5,10 @@
         "homepage": "https://input-output-hk.github.io/haskell.nix",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "33cd29ee330d34c8c99a9ce56fb3529b44cf3224",
-        "sha256": "1jgwz2iahvn43w398aanm4djzjmr5a2hcv1ijzi9vh79circ7ffz",
+        "rev": "ab2f5a9b6d8cb1b18810194d9f4a6208710c358c",
+        "sha256": "1j3zwrrmnigl44lqdiyywwhj5m0wb4v6bpl89v1wp31vxwyyf7rv",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/33cd29ee330d34c8c99a9ce56fb3529b44cf3224.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/ab2f5a9b6d8cb1b18810194d9f4a6208710c358c.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "iohk-nix": {