Update sbt-mdoc to 2.8.2 (#451)

Author: scala-steward

project/plugins.sbt

@@ -4,4 +4,4 @@ addSbtPlugin("com.github.sbt" % "sbt-release" % "1.4.0")
 addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")
 addSbtPlugin("org.xerial.sbt" % "sbt-sonatype" % "3.12.2")
 addSbtPlugin("com.47deg" % "sbt-microsites" % "1.4.4")
-addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.8.1")
+addSbtPlugin("org.scalameta" % "sbt-mdoc" % "2.8.2")