Update mdoc_2.12.12, sbt-mdoc to 2.2.18

Author: 47erbot

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("com.eed3si9n"              % "sbt-buildinfo"            % "0.10.0")
-addSbtPlugin("org.scalameta"             % "sbt-mdoc"                 % "2.2.17")
+addSbtPlugin("org.scalameta"             % "sbt-mdoc"                 % "2.2.18")
 addSbtPlugin("org.scalameta"             % "sbt-scalafmt"             % "2.4.2")
 addSbtPlugin("com.geirsson"              % "sbt-ci-release"           % "1.5.5")
 addSbtPlugin("de.heikoseeberger"         % "sbt-header"               % "5.6.0")