Replace platforms.linux with platforms.darwin for expressions that compile on darwin too (too restrictive platforms)

pkgs/development/python-modules/pychromecast/default.nix

@@ -18,6 +18,6 @@ buildPythonPackage rec {
     homepage    = https://github.com/balloob/pychromecast;
     license     = licenses.mit;
     maintainers = with maintainers; [ abbradar ];
-    platforms   = platforms.linux;
+    platforms   = platforms.unix;
   };
 }