Update sbt-scoverage to 2.3.1 (#551)

Author: scala-steward

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("com.github.sbt" % "sbt-release"    % "1.4.0")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"   % "2.5.4")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.9.2")
-addSbtPlugin("org.scoverage"  % "sbt-scoverage"  % "2.3.0")
+addSbtPlugin("org.scoverage"  % "sbt-scoverage"  % "2.3.1")
 addSbtPlugin("org.typelevel"  % "sbt-tpolecat"   % "0.5.2")