Dependency management switch from dep to mod

[prometherion]

I'd like to provide some contributions and the first thing I noticed is that the package is still relying on dep rather than Go mod that is provided since 1.11.

JFI I'm happy to take care of this issue.

What would you like to be added?

go.{mod.sum} files following the go mod shadow vendoring (no more need to commit vendor files, too).

Why is this needed?

dep is no more widely used, also considering that the vendoring is fully provided by Go itself without the need to rely on a third-party package.