MAINT: Fix for upstream changes in PyMC3 notebook
MAINT: Fix for upstream changes in PyMC3 notebook

Use current syntax in PyMC3 notebooks

closes #7398

statsmodels/statsmodels,josef-pkt/statsmodels,statsmodels/statsmodels,josef-pkt/statsmodels,statsmodels/statsmodels,josef-pkt/statsmodels,statsmodels/statsmodels,statsmodels/statsmodels,bashtage/statsmodels,bashtage/statsmodels,bashtage/statsmodels,bashtage/statsmodels,bashtage/statsmodels,bashtage/statsmodels,josef-pkt/statsmodels,statsmodels/statsmodels,josef-pkt/statsmodels,josef-pkt/statsmodels