Update outdated list of Pythons tested against
Update outdated list of Pythons tested against

- cPython 3.3 support was dropped in 0.10.0
- cPython 3.4 support was dropped in 0.12.4
- cPython 3.6 support was added in 0.8.4
- cPython 3.7 support was added in 0.12.1
- cPython 3.8 support was added in 0.12.4

kvesteri/postgresql-audit