Add unionfs-fuse and ntfs-3g to the channel

pkgs/tools/filesystems/ntfs-3g/default.nix

···
     homepage = http://www.tuxera.com/community/;
     description = "FUSE-base NTFS driver with full write support";
     maintainers = [ stdenv.lib.maintainers.urkud ];
+    platforms = stdenv.lib.platforms.linux;
   };
 }

pkgs/tools/filesystems/unionfs-fuse/default.nix

···
     homepage = http://podgorny.cz/moin/UnionFsFuse;
     license = stdenv.lib.licenses.bsd3;
     maintainers = [ stdenv.lib.maintainers.shlevy ];
+    platforms = stdenv.lib.platforms.linux;
   };
 }