License expiration date. The format is YYYYMMDD, so for example if the license currently in use expired on July 20,
2018, the result would be 20180720. If the license has no expiration date, the result will be 99999999.

This attribute is available for node licenses and for clients of a Gurobi Compute Server. Unfortunately, this attribute
isn't available for clients of a Gurobi Token Server.