Update sbt-pgp to 2.3.1

Author: scalikejdbc-bot[bot]

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.5.2")
 addSbtPlugin("org.playframework" % "sbt-plugin" % "3.0.6")
-addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.0")
+addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")
 
 scalacOptions ++= Seq("-deprecation", "-unchecked", "-language:_")