Update scala-library to 2.13.15 (#76)

Co-authored-by: lunatech-scala-steward[bot] <166295259+lunatech-scala-steward[bot]@users.noreply.github.com>

Author: lunatech-scala-steward[bot]

build.sbt

@@ -6,7 +6,7 @@ Global / onChangedBuildSource := ReloadOnSourceChanges
 
 lazy val root = (project in file(".")).enablePlugins(PlayScala)
 
-scalaVersion := "2.13.14"
+scalaVersion := "2.13.15"
 
 libraryDependencies ++= Seq(
   guice, ws,