Update sbt-wartremover, wartremover to 3.1.8

Author: scala-steward

project/plugins.sbt

@@ -11,5 +11,5 @@ addSbtPlugin("io.kevinlee" % "sbt-github-pages" % "0.14.0")
 addSbtPlugin("nl.gn0s1s" % "sbt-dotenv" % "3.0.0")
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.2")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.0.12")
-addSbtPlugin("org.wartremover" % "sbt-wartremover" % "3.1.7")
+addSbtPlugin("org.wartremover" % "sbt-wartremover" % "3.1.8")
 addSbtPlugin("org.xerial.sbt" % "sbt-sonatype" % "3.11.1")