Use multi-stage builds and remove apt and pip caches

Changelog for 0.3.2:

• PR #62 feat: user multi-stage builds and remove apt and pip caches by @LucasRoesler

Commits
79b444b feat: user multi-stage builds and remove apt and pip caches by @LucasRoesler
d3cd007 Upgrade to of-watchdog 0.9.8 for the readiness endpoint by @alexellis

Changes: 0.3.1...0.3.2

Generated by Derek