Update sbt-mdoc to 2.8.1 (#70)

Co-authored-by: scala-steward <scala-steward>

Author: softwaremill-ci

project/plugins.sbt

@@ -2,5 +2,5 @@ val sbtSoftwareMillVersion = "2.1.0"
 
 addSbtPlugin("com.softwaremill.sbt-softwaremill" % "sbt-softwaremill-common" % sbtSoftwareMillVersion)
 addSbtPlugin("com.softwaremill.sbt-softwaremill" % "sbt-softwaremill-publish" % sbtSoftwareMillVersion)
-addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.8.0")
+addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.8.1")
 addSbtPlugin("io.spray" % "sbt-revolver" % "0.10.0")