update firebase/php-jwt to 4.0

[ashbeats]

No description provided.

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[ashbeats]

ok. it's signed.

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CLAs look good, thanks!

[bshaffer]

Is there a specific reason you need Firebase 4.0?

[boredom2]

I need it:-)
The Microsoft Azure SDK has been updated and is only compatible with JWT 4.0 now.
So its really complicated to include Google and Azure with different dependencies for this Lib.

[ashbeats]

I'm using laravel/spark, which requires firebase v4.0.

[tomschlick]

Another request for this from another laravel/spark user. Can't upgrade spark without it.

Doesn't look like there are any breaking changes in the 3.0->4.0 migration so are there any reasons not to upgrade?

[etremblay]

This PR would be very appreciated !

[bshaffer]

This change will not have an affect as long as google/auth requires ~3.0. This change should fix that: googleapis/google-auth-library-php#137. I will merge this as soon as this is tagged and updated

[tomschlick]

Any update? googleapis/google-auth-library-php#137 has been merged.

[bshaffer]

This was merged into master in #1082