6.8

Changelog

• Add Python 3.8 support (for Grocker command).
• Add support for buster/3.8 runtime.
• Add support for buster/3.7 runtime.
• Add support for alpine/3 runtime and use it by default.
• Deprecate stretch/3.7 runtime (deprecation warning).
• Deprecate alpine/3.6 runtime (deprecation warning)
• Drop Python 3.4 support since it is not supported anymore (breaking change).