PyBrain: Mark as broken

It's broken on all versions of Python (I've tried 2.7, 3.4, 3.5, 3.6)

I think the root cause is that PyBrain is not working with numpy >= 1.12.0 as I reported here:
https://github.com/pybrain/pybrain/issues/217

(The relevant release notes may be found here):
https://docs.scipy.org/doc/numpy-1.12.0/release.html#compatibility-notes

The PyBrain github repo does not seem very active (last commit 18 months ago, last release 3 years),
so I have some doubts as to whether this will be fixed any time soon.

I suppose an alternative solution could be to reintroduce the explicit dependency to numpy 1.11. But,
this is not entirely trivial: in c9b4a2f319, the versions 1.10, 1.11, 1.12 were folded into a single version.
Also, the numpy dependency is not a direct one, but is implied via scipy

pkgs/top-level/python-packages.nix

@@ -26882,6 +26882,7 @@ EOF
       description = "Modular Machine Learning Library for Python";
       license = licenses.bsd3;
       maintainers = with maintainers; [ NikolaMandic ];
+      broken = true; # See https://github.com/NixOS/nixpkgs/pull/29198
     };
   };