Upgrading tox envs to python3.8 (#426)
Upgrading tox envs to python3.8 (#426)

Python3.8 is now stable, and we should run the common tasks under 3.8
instead of 3.7
open-telemetry/opentelemetry-python-contrib,open-telemetry/opentelemetry-python-contrib,open-telemetry/opentelemetry-python-contrib