[cli] Changes `fog --version` short option to `-v`

Looking at a number of similar Ruby based tools, Bundler, Rubygems, Pry
and IRB all use lowercase v for the short option for `--version`

Ruby itself uses `-v` for verbose but without any further arguments
prints the version and exits.
Merge pull request #1927 from fog/change_version_short_option

[cli] Changes `fog --version` short option to `-v`