Support for more CI platforms

[wezm]

Given the content of https://rust-digger.code-maven.com/about-ci I assume this is a known issue but I thought I'd open an issue to track support for other CI providers. Specifically I use Cirrus CI, which can probably be identified by the presence of .cirrus.yml or .cirrus.star in the root of the repo.

https://github.com/szabgab/rust-digger/blob/79de34a90bbe88a3eb4d76bb405a2061d6aa2c8a/src/vcs.rs#L88-L101