Update mdoc, sbt-mdoc to 2.5.3 (#108)

Author: scala-steward

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.scoverage"  % "sbt-scoverage"  % "2.0.12")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"   % "2.5.2")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.12")
-addSbtPlugin("org.scalameta"  % "sbt-mdoc"       % "2.5.2")
+addSbtPlugin("org.scalameta"  % "sbt-mdoc"       % "2.5.3")
 addDependencyTreePlugin