Fix 'Polynomial regular expression used on uncontrolled data code' scanning alert

[stefannibrasil]

https://github.com/faker-ruby/faker/security/code-scanning/14
https://github.com/faker-ruby/faker/security/code-scanning/13

[stefannibrasil]

Thanks! We are down to 1. Reopening this until that one is fixed: https://github.com/faker-ruby/faker/security/code-scanning/11