essentia-extractor: fix eval on darwin

pkgs/tools/audio/essentia-extractor/default.nix

@@ -6,22 +6,20 @@ let
   };
 
   sha_table = {
-    "x86_64-linux" =
-      "d9902aadac4f442992877945da2a6fe8d6ea6b0de314ca8ac0c28dc5f253f7d8";
-    "i686-linux" =
-      "46deb0a053b4910c4e68737a7b6556ff5360260c8f86652f91a0130445f5c949";
+    "x86_64-linux" = "d9902aadac4f442992877945da2a6fe8d6ea6b0de314ca8ac0c28dc5f253f7d8";
+    "i686-linux" = "46deb0a053b4910c4e68737a7b6556ff5360260c8f86652f91a0130445f5c949";
   };
 
-  arch = arch_table.${stdenv.system};
-  sha = sha_table.${stdenv.system};
+  throwSystem = throw "Unsupported system: ${stdenv.system}";
+  arch = arch_table.${stdenv.system} or throwSystem;
 in
 stdenv.mkDerivation rec {
   pname = "essentia-extractor";
   version = "2.1_beta2";
 
   src = fetchurl {
-    url = "ftp://ftp.acousticbrainz.org/pub/acousticbrainz/essentia-extractor-v${version}-${arch}.tar.gz";
-    sha256 = sha;
+    url = "https://ftp.acousticbrainz.org/pub/acousticbrainz/essentia-extractor-v${version}-${arch}.tar.gz";
+    sha256 = sha_table.${stdenv.system} or throwSystem;
   };
 
   unpackPhase = "unpackFile $src ; export sourceRoot=.";