Add -release 8 scalac option (#3006)

Author: regadas

build.sbt

@@ -168,6 +168,7 @@ val commonSettings = Sonatype.sonatypeSettings ++ assemblySettings ++ Seq(
       Seq()
     }
   },
+  Compile / doc / scalacOptions --= Seq("-release", "8"),
   scalacOptions in (Compile, doc) ++= Scalac.compileDocOptions.value,
   javacOptions ++= Seq("-source", "1.8", "-target", "1.8", "-Xlint:unchecked"),
   javacOptions in (Compile, doc) := Seq("-source", "1.8"),
@@ -1074,6 +1075,7 @@ lazy val `scio-repl`: Project = project
   .settings(commonSettings)
   .settings(macroSettings)
   .settings(
+    scalacOptions --= Seq("-release", "8"),
     libraryDependencies ++= Seq(
       "org.scala-lang.modules" %% "scala-collection-compat" % scalaCollectionCompatVersion,
       "org.apache.beam" % "beam-runners-direct-java" % beamVersion,

project/ScalacOptions.scala

@@ -20,6 +20,8 @@ import sbt._, Keys._
 object Scalac {
   // see: https://tpolecat.github.io/2017/04/25/scalac-flags.html
   val baseOptions = List(
+    "-release",
+    "8",
     "-target:jvm-1.8",
     "-deprecation", // Emit warning and location for usages of deprecated APIs.
     "-feature", // Emit warning and location for usages of features that should be imported explicitly.