Specify that Java 1.8 is required for compile

The ETL relies on Spark 2.3.3 which supports only Java 8.

See [1] for more details.

[1] https://community.cloudera.com/t5/Community-Articles/Spark-and-Java-versions-Supportability-Matrix/ta-p/383669

Change-Id: I75db9b172f7a9aca7829d1e6920032d396b1da46

project/SharedSettings.scala

diff --git a/project/SharedSettings.scala b/project/SharedSettings.scala
index c3426ba..8c30929 100644
--- a/project/SharedSettings.scala
+++ b/project/SharedSettings.scala
@@ -30,6 +30,7 @@
 
   lazy val commonSettings: Seq[Def.Setting[_]] = Seq(
     scalaVersion := "2.11.12",
+    javacOptions in Compile ++= Seq("-source", "8", "-target", "8"),
     organization := "gerritforge",
     parallelExecution in Test := false,
     fork in Test := true,