build(deps): bump github.com/cpuguy83/go-md2man/v2 from 2.0.5 to 2.0.6 (#2206)

fix compatibility with go versions before go1.17

diff: https://github.com/cpuguy83/go-md2man/compare/v2.0.5...v2.0.6

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>