Fix flake8 issues with OtsuMultipleThreshold.py
Fix flake8 issues with OtsuMultipleThreshold.py

mathturtle/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,thewtex/tomviz,cryos/tomviz,thewtex/tomviz,cjh1/tomviz,cryos/tomviz,thewtex/tomviz,cjh1/tomviz,cryos/tomviz,cjh1/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,OpenChemistry/tomviz