python3Packages.scikit-bio: mark as x86_64-only

pkgs/development/python-modules/scikit-bio/default.nix

···
     homepage = "http://scikit-bio.org/";
     description = "Data structures, algorithms and educational resources for bioinformatics";
     license = licenses.bsd3;
+    platforms = [ "x86_64-linux" "x86_64-darwin" ];
     maintainers = [ maintainers.costrouc ];
   };
 }