Log Message:
security/ruby-metasploit-model: update to 3.1.3

pkgsrc change: add LICENSE.

No release note nor changelog.  Here are quote from commit log.

3.1.0 (2020-10-05)

* Added Address Format Validator And Updated Spec Testing
* Update app/validators/password_is_strong_validator.rb

3.1.1 (2020-10-05)

* update dummy schema.rb for automation

3.1.2 (2020-10-05)

* update authors and do not include `bin` in gem

3.1.3 (2020-12-01)

* update to support Ruby 2.7