Update scala-library from 2.12.14 to 2.12.15 (#693)

Co-authored-by: Scala Steward <[email protected]>

Author: jakubjanecek

project/BuildSettings.scala

@@ -28,7 +28,7 @@ object BuildSettings {
     licenses := Seq("MIT" -> url("https://raw.githubusercontent.com/avast/scala-server-toolkit/master/LICENSE")),
     developers := List(Developer("jakubjanecek", "Jakub Janecek", "[email protected]", url("https://www.avast.com"))),
     scalaVersion := "2.13.6",
-    crossScalaVersions := List(scalaVersion.value, "2.12.14"),
+    crossScalaVersions := List(scalaVersion.value, "2.12.15"),
     fork := true,
     libraryDependencies ++= Seq(
       compilerPlugin(Dependencies.kindProjector),