Merge branch 'master' of https://github.com/rocker-org/rocker-versioned

Makefile

r-ver/3.1.0.Dockerfile

r-ver/3.1.0/hooks/post_push

r-ver/3.1.2.Dockerfile

r-ver/3.1.2/hooks/post_push

r-ver/3.1.3.Dockerfile

r-ver/3.1.3/hooks/post_push

r-ver/3.2.0.Dockerfile

r-ver/3.2.0/hooks/post_push

r-ver/3.2.1.Dockerfile

r-ver/3.2.1/hooks/post_push

r-ver/3.2.2.Dockerfile

r-ver/3.2.2/hooks/post_push

r-ver/3.2.3.Dockerfile

r-ver/3.2.3/hooks/post_push

r-ver/3.2.4.Dockerfile

r-ver/3.2.4/hooks/post_push

r-ver/3.2.5.Dockerfile

r-ver/3.2.5/hooks/post_push

r-ver/3.3.0.Dockerfile