[gherkin-perl] Add dependency on Getopt::Long for `bin/gherkin`
[gherkin-perl] Add dependency on Getopt::Long for `bin/gherkin`

Note that `bin/gherkin` also depends on Pod::Usage, but that is
a CORE module, meaning it comes with Perl and doesn't need separate
installation.

cucumber/gherkin-perl,cucumber/gherkin-perl