Revert "Update minimum required version of PHPUnit to 6.5.0 to fix broken builds on PHP 7.2." and hope 4a33cd14bc can fixes this problem too.
Revert "Update minimum required version of PHPUnit to 6.5.0 to fix
broken builds on PHP 7.2." and hope 4a33cd14bc can fixes this problem
too.

This reverts commit bb02a39

apigee/apigee-client-php