Add sbt-updates plugin

Use `sbt dependencyUpdates` to learn about dependency updates.

Author: Christos KK Loverdos

project/plugins.sbt

@@ -6,5 +6,6 @@ addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.0.6")
 addSbtPlugin("com.thoughtworks.sbt-api-mappings" % "sbt-api-mappings" % "latest.release")
 addSbtPlugin("uk.co.josephearl" % "sbt-verify" % "0.3.0-SNAPSHOT")
 addSbtPlugin("com.thesamet" % "sbt-protoc" % "0.99.12")
+addSbtPlugin("com.timushev.sbt" % "sbt-updates" % "0.3.4")
 
 libraryDependencies += "com.trueaccord.scalapb" %% "compilerplugin" % "0.6.6"