Updated baseline

1.538 is over 13 months old and tests cannot even be run on Java 8. Updating to the next newer LTS.
When doing automated or interactive testing, I do not want to be wasting my time tracking down and working around bugs which were already fixed in the LTS update that people ought to be running anyway. Otherwise there is no purpose in using an LTS-related version at all; could use 1.557 as the baseline in this case, which then would block out 1.554.3 users. (1.554 does _not_ run on Java 8.)