Bump goenv module.

This disables the goenv install and uninstall commands. See
https://github.com/gds-operations/puppet-goenv/pull/2 for details.
Remove trailing / from forge line.

This was causing librarian-puppet to return the somewhat cryptic error:

Cannot bounce Puppetfile.lock!
Merge pull request #207 from alphagov/bump_goenv_module

Bump goenv module.