Support jwt gem version 3

[lostie]

Checklist

• I have looked into the Readme and Examples, and have not found a suitable solution or answer.
• I have looked into the API documentation and have not found a suitable solution or answer.
• I have searched the issues and have not found a suitable solution or answer.
• I have searched the Auth0 Community forums and have not found a suitable solution or answer.
• I agree to the terms within the Auth0 Code of Conduct.

Describe the problem you'd like to have solved

Currently the gemspec is locked to version 2 only

ruby-auth0/auth0.gemspec

Line 20 in 45cef15

s.add_runtime_dependency 'jwt', '~> 2.7'

Describe the ideal solution

Update the jwt dependency to also support version 3, maybe something like:

s.add_runtime_dependency 'jwt', '>= 2.7', '< 4.0'