Boltzmann brain requires an unreleased version of paganini

[Kerl13]

It seems that the current version of boltzmann-brain requires the development version of paganini.

Running bb-compile with the most recently released version of paganini (1.3.3) fails with :

[ERR] (01-07-2022 19:32:19) SolverFailure "/home/martin/.local/lib/python3.10/site-packages/cvxpy/problems/problem.py:1337: UserWarning: Solution may be inaccurate. Try another solver, adjusting the solver settings, or solve with verbose=True for more information.\n  warnings.warn(\nTraceback (most recent call last):\n  File \"<stdin>\", line 19, in <module>\nAttributeError: 'Specification' object has no attribute 'ddg'\n" {def v0; def v1; v1 := 0 + v0 + v0**2 * v1 + v0 * v1**2} [v0; v1] Target variable: v1.

whereas it works fine the latest git version.

I don't think it's a problem (this is the development version of boltzmann-brain anyway) but I think it would be nice to maybe update the readme but mostly to update the nix file. It currently pins the 1.3.3 version of paganini, which misled me.