pythonPackages.websockify: Needs to propagate numpy

pkgs/top-level/python-packages.nix

···
       md5 = "29b6549d3421907de4bbd881ecc2e1b1";
     };
 
-    buildInputs = [ numpy ];
+    propagatedBuildInputs = [ numpy ];
 
     meta = {
       description = "WebSockets support for any application/server";