Bump up sbt-jmh to 0.2.21
Bump up sbt-jmh to 0.2.21

With this change, we'll use JMH 1.17.4.

martijnhoekstra/scala,scala/scala,martijnhoekstra/scala,scala/scala,martijnhoekstra/scala,lrytz/scala,lrytz/scala,lrytz/scala,martijnhoekstra/scala,scala/scala,scala/scala,martijnhoekstra/scala,scala/scala,lrytz/scala,lrytz/scala,lrytz/scala,scala/scala,martijnhoekstra/scala