Run tests against python 3.6.8 since TFDS now requires at least 3.6.5.
Run tests against python 3.6.8 since TFDS now requires at least 3.6.5.

PiperOrigin-RevId: 334713818
Change-Id: I98db05c216a7392782d0538d6ec92b280ed6ded2

tensorflow/gan,tensorflow/gan