License is missing

[Nghi93]

Can you add a LICENSE.md please?

[zealot128]

This project is only a fork of a fork of a .... of https://github.com/macarthy/simple-captcha-mirror

That seems to be MIT licensed, so nothing against keeping that license.
Would you like to add a PR with the license file? Maybe also a metadata field in the *gemspecs https://guides.rubygems.org/specification-reference/?

[Nghi93]

#68

[Nghi93]

Could you release a new version please.