Update NiFi to 1.13.2 and NiFi-Registry to 0.8.0
Update NiFi and client to 1.13.2
Update Registry and client to 0.8.0
Minor spelling and linting fixes
Removed travisCI build indicator as TravisCI itself has been broken for a while, will move to new build service
Removed extraneous nifidev and registrydev containers from tox-full docker-compose definition
Note that Python 3.9 has SSL issues, but the library is testing as normal with 3.5-3.8/2.7.