modified pl-checkbox.py after running lint-python
modified pl-checkbox.py after running lint-python

rbessick5/PrairieLearn,mwest1066/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,mwest1066/PrairieLearn,mwest1066/PrairieLearn,mwest1066/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,mwest1066/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn