Update scala-library to 2.13.15 (#590)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: scala-steward

build.sbt

@@ -1,7 +1,7 @@
 Global / onChangedBuildSource := IgnoreSourceChanges // not working well with webpack devserver
 
 ThisBuild / version      := "0.1.0-SNAPSHOT"
-ThisBuild / scalaVersion := "2.13.14"
+ThisBuild / scalaVersion := "2.13.15"
 
 Global / excludeLintKeys += webpackDevServerPort // TODO: