spotify-ripper: mark as unfree

Allows building CI as free-only following requirements of upstream.

.travis.yml

@@ -7,7 +7,6 @@ os: linux
 env:
   global:
     - CACHIX_CACHE="xeals"
-    - NIXPKGS_ALLOW_UNFREE="1"
     - NUR_REPO="xeals"
 
 jobs:

pkgs/tools/misc/spotify-ripper/default.nix

@@ -57,6 +57,7 @@ python2Packages.buildPythonApplication rec {
       to WAV, FLAC, Ogg Vorbis, Opus, AAC, and MP4/M4A.
     '';
     homepage = "https://github.com/hbashton/spotify-ripper";
-    license = stdenv.lib.licenses.mit;
+    # spotify-ripper itself is MIT, but the upstream libspotify is unfree.
+    license = stdenv.lib.licenses.unfree;
   };
 }