Update sbt-scoverage to 2.4.0 (#298)

Author: scala-steward

project/plugins.sbt

@@ -1,6 +1,6 @@
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.5")
 
-addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.3.1")
+addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.4.0")
 
 addSbtPlugin("ch.epfl.scala" % "sbt-version-policy" % "3.2.1")