emcee 3.1.5 incompatible with numpy < 1.25.0

[MuellerSeb]

Before numpy 1.25, there was no exceptions namespace in numpy: https://numpy.org/doc/1.25/release/1.25.0-notes.html#numpy-now-has-an-np-exceptions-namespace

This makes the latest version of emcee (3.1.5) incompatible with these versions as mentioned here: #515 (comment)