HeteroscedasticSNGPLayer error with num_classes=2

[Krasner]

HeteroscedasticSNGPLayer inherits from MCSoftmaxDenseFA which has an assert check:

edward2/edward2/tensorflow/layers/heteroscedastic.py

Line 605 in 2a85212

assert num_classes > 2

but itself is written in a way that should accept num_classes=2:

edward2/edward2/tensorflow/layers/hetsngp.py

Line 232 in 2a85212

if self._num_classes == 2: