Primes v1.2.1

[moebius-rex]

Primes v1.2.1 is a 1.2.0 patch release that includes the following changes:

• Migrate from apt-get install to apt install in ubuntu.dockerfile
• Support use of Linux distro's default shell when attaching to a Docker container
• Support chaining of actions in go/sieve/sieve.go and use in go/app2/app.go
• Remove go/app2/app.go negative range check since it's already done in go/sieve/sieve.go
• Set then unset GOFLAGS = -compiler gccgo in go Makefiles as a reminder to try gccgo once the Ubuntu docker install works
• Add a note to DOCKER.md explaining why Docker-in-Docker isn't supported

---

This discussion was created from the release Primes v1.2.1.