flake8 linter

boundaries/__init__.py

boundaries/boundaryconditions.py

chapman_enskog/chapman_enskog.py

chapman_enskog/chapman_enskog_higher_order.py

chapman_enskog/chapman_enskog_steady_state.py

chapman_enskog/derivative.py

creationfunctions.py

cumulants.py

fieldaccess.py

forcemodels.py

geometry.py

innerloopsplit.py

methods/__init__.py

methods/abstractlbmethod.py

methods/conservedquantitycomputation.py

methods/creationfunctions.py

methods/cumulantbased.py

methods/entropic.py

methods/momentbased.py

phasefield/cahn_hilliard_lbm.py