Add -deprecation

Author: alexarchambault

build.sbt

@@ -24,6 +24,7 @@ lazy val isJava9OrMore = sys.props.get("java.version").exists(!_.startsWith("1."
 lazy val interface = project
   .enablePlugins(SbtProguard)
   .settings(
+    scalacOptions += "-deprecation",
     moduleName := {
       val former = moduleName.value
       val sv = scalaVersion.value

project/Settings.scala

@@ -37,7 +37,7 @@ object Settings {
   lazy val shared = Seq(
     scalaVersion := scala213,
     crossScalaVersions := Seq(scala213, scala212),
-    scalacOptions ++= Seq("--release", "8"),
+    scalacOptions ++= Seq("--release", "8", "-deprecation"),
     javacOptions ++= Seq(
       "-source", "8",
       "-target", "8",