ThreadlocalRandom instead of ThreadLocal

Hey,

While reading the changes in the newest releases and the code for it, I saw this comment. https://github.com/google/flogger/blob/master/api/src/main/java/com/google/common/flogger/SamplingRateLimiter.java#L55 If I understand the build system correct flogger requires at least java 8, so ThreadLocalRandom(https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ThreadLocalRandom.html) or `ThreadLocal.withInitial` is available. Is the comment a relict of the past and the code could be changed?