Update kokoro/docs/publish-python.sh
Update kokoro/docs/publish-python.sh

Update kokoro/docs/publish-python.sh to use the latest version of protoc and python.

This will make [the python doc-publishing job](https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod:cloud-devrel%2Fclient-libraries%2Fprotobuf%2Fdocs%2Fpython) pass again.
google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf