make the cache ttl compatible with Symfony

[nanofelis]

The cache used in the FirebaseJwtAdapter is not compatible with symfony/cache because it uses a Carbon date for the cache item TTL but Symfony only accepts an integer or a DateInterval.

https://github.com/symfony/cache/blob/364fc90734230d936ac2db8e897cc03ec8497bbb/CacheItem.php#L90

    public function expiresAfter($time): self
    {
        if (null === $time) {
            $this->expiry = null;
        } elseif ($time instanceof \DateInterval) {
            $this->expiry = microtime(true) + \DateTime::createFromFormat('U', 0)->add($time)->format('U.u');
        } elseif (\is_int($time)) {
            $this->expiry = $time + microtime(true);
        } else {
            throw new InvalidArgumentException(sprintf('Expiration date must be an integer, a DateInterval or null, "%s" given.', get_debug_type($time)));
        }

        return $this;
    }

So we get the following exception when setting the TTL:

{
    class: "Symfony\\Component\\Cache\\Exception\\InvalidArgumentException"
    detail: "Expiration date must be an integer, a DateInterval or null, \"Carbon\\Carbon\" given."
}

Issue : #107

[selvaramj]

i tried this one in my local, its working fine with symfony, please validate & release this code.