Go 1.16 reached end of life, so update to the current version of Go, but also
run CI on the previous version (which is still supported).
We should probably also decide wether or not we want the Dockerfiles to pin to
a specific minor version; this makes the releases more deterministic.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Vndr has a simpler configuration and allows pointing to forked
packages. Additionally other docker projects are now using
vndr making vendoring in distribution more consistent.
Updates letsencrypt to use fork.
No longer uses sub-vendored packages.
Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
