Relax dependnecy on JWT

[byroot]

jwt is a very popular depdency, and numerous other gems are yet to be updated to allow jwt 3.x.

Since web-push works fine with jwt 2.x, I see no reason to prevent installation.

[byroot]

👋 @collimarco sorry for the ping, but could you consider this PR?

[collimarco]

@byroot Thanks for your contribution. Personally I don't see much value in this change: jwt v3 was released 1 year ago and this gem reflects that... Otherwise I would need to create a new release for this change (which isn't relevant for other users) and then another future release again to drop support for it. As a temporary workaround, until you update jwt in your application, which is the recommended approach, you can use v3.0.1, which uses jwt v2. The newer versions of this gem are just version upgrades of gem dependencies, so if you don't want them, just keep using the older version for some time.

[byroot]

Personally I don't see much value in this change

The value is that I'm currently fighting with two other gems that have a dependency on jwt ~> 2.x, but initially what I wanted to do was to upgrade to openssl 4.x, which I can't because web-push, so I want #19

The value of this change is to get your users out of dependency hell, by allowing more progressive upgrades.