Remove travis testing against pypy3, add 3.6. (#398)
Remove travis testing against pypy3, add 3.6. (#398)

pypy3 runs against Python 3.2 which is no longer supported. When we find
a way to install the latest version of pypy3 (which runs against python
3.5) we can add testing for it back.
rjschwei/compute-image-packages,illfelder/compute-image-packages,rjschwei/compute-image-packages,wrigri/compute-image-packages,GoogleCloudPlatform/compute-image-packages,illfelder/compute-image-packages,wrigri/compute-image-packages,zmarano/compute-image-packages,zmarano/compute-image-packages,wrigri/compute-image-packages,wrigri/compute-image-packages