Update Golang from 1.13 to 1.16 by replacing it with the official tdewolff/minify image

Updates Golang from 1.13 to 1.16, which is used on use of minify, by using the upstream official Docker image.

Also enables us to keep up-to-date in terms of Go version.

https://github.com/tdewolff/minify/blob/master/Dockerfile

https://hub.docker.com/r/tdewolff/minify

Part of &5546 (closed)