Update scala-library, scala-reflect to 2.12.15 (#403)

Author: scala-steward

build.sbt

@@ -26,7 +26,7 @@ lazy val commonSettings =
   Seq(
     organization := "org.mockito",
     //Load version from the file so that Gradle/Shipkit and SBT use the same version
-    crossScalaVersions := Seq(currentScalaVersion, "2.12.14", "2.11.12"),
+    crossScalaVersions := Seq(currentScalaVersion, "2.12.15", "2.11.12"),
     scalafmtOnCompile := true,
     scalacOptions ++= Seq(
       "-unchecked",