composer.json - Require firebase/php-jwt (v3 - v5)

composer.json - Require firebase/php-jwt (v3 - v5)

When this version range?

* It's a fairly popular package, so may be prone to conflicts. A wide range is desireable.
* The low end (v3) is 5+ years old. The high end (v5) is current latest.
* If you 'git diff' between v3=>v4=>v5, the changes are fairly incrementaly. They
  add more crypto algorithms, twiddle docblocks and PHP environment compatibility,
  and introduce a service we don't need (JWK). The main interfaces all look the same.
* The only notable bit was that some exceptions were recategorized, but the broad taxonomy
  of exceptions still seems similar.