add lichking to check licenses

nix/sources.json

@@ -1,4 +1,16 @@
 {
+    "cargo-lichking": {
+        "branch": "master",
+        "description": "Automated license checking for rust. cargo lichking is a Cargo subcommand that checks licensing information for dependencies.",
+        "homepage": "",
+        "owner": "Nemo157",
+        "repo": "cargo-lichking",
+        "rev": "4cd86f04c8a17e9f6b3dc1079ef7edbc7fa584ed",
+        "sha256": "151p5mxmpnvk3c202qdbc19qib35q9cbc0446999l8gf06hwjmbj",
+        "type": "tarball",
+        "url": "https://github.com/Nemo157/cargo-lichking/archive/4cd86f04c8a17e9f6b3dc1079ef7edbc7fa584ed.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "gitignore": {
         "branch": "master",
         "description": "Nix function for filtering local git sources",

shell.nix

@@ -3,6 +3,9 @@ let
   sources = import ./nix/sources.nix;
   nixpkgs = import sources.nixpkgs { };
   niv = import sources.niv { };
+  naersk = nixpkgs.callPackage sources.naersk { };
+
+  cargo-lichking = naersk.buildPackage sources.cargo-lichking;
 in with nixpkgs;
 stdenv.mkDerivation {
   name = "elm-forbid-import";
@@ -12,6 +15,7 @@ stdenv.mkDerivation {
 
     # Rust
     cargo
+    cargo-lichking
     cargo-watch
     rustPackages.clippy
     rustPackages.rustfmt