Upgrade Play Framework 2.6.13 => 2.6.15 (#341)
Upgrade Play Framework 2.6.13 => 2.6.15 (#341)

- 'addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.6.13")' => 'addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.6.15")'
flowcommerce/lib-event