BUG: 6.11.0 breaks for PHP 7.2

[mborahilly]

Since https://github.com/firebase/php-jwt/issues/577 was merged, 6.11.0 will break. Currently, if this package is pulled as a transitive dependency it does not properly block to supported versions. Ex, google/apiclient.

6.10.2 is the last working version for PHP 7.2. As a workaround lower the version to 6.10.2. I am aware that as of 6.10.1, PHP 7.4 support was dropped, and that 6.4.0 is the last PHP 7.2 supported version. This bad version mapping may be an issue with google/apiclient rather than this package, but posting this here for anyone else on legacy PHP for the interim.