Update sbt-jmh to 0.4.8 (#698)

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -6,4 +6,4 @@ addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.4.0")
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.8.0")
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % "0.8.0")
-addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.7")
+addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.8")