Fix `Examples/HeisenbergJ1J2/heisenbergJ1J2.py`
Created by: attila-i-szabo
There was one small bug in this example that I hadn't noticed when copying the source from the paper. Heisenberg
defaults to sign_rule=False
for coloured graphs, and you'd need a list of sign_rule
s to override it, so the old version would error out on this line. This is now fixed in the paper too; the current version runs without errors.