diff --git a/build.sbt b/build.sbt
index 0422e1a..ec53415 100644
--- a/build.sbt
+++ b/build.sbt
@@ -5,11 +5,11 @@ organization := "com.sclasen"
 name := "akka-zk-cluster-seed"
 version := "0.1.11-SNAPSHOT"
 
-scalaVersion := "2.12.4"
-crossScalaVersions := Seq(scalaVersion.value, "2.11.11")
+scalaVersion := "2.13.0"
+crossScalaVersions := Seq(scalaVersion.value, "2.12.8", "2.11.12")
 
-val akkaVersion = "2.5.9"
-val akkaHttpVersion = "10.0.11"
+val akkaVersion = "2.5.+"
+val akkaHttpVersion = "10.1.+"
 
 val akkaDependencies = Seq(
   "com.typesafe.akka" %% "akka-actor" % akkaVersion,
@@ -25,7 +25,7 @@ val exhibitorOptionalDependencies = Seq(
   "com.typesafe.akka" %% "akka-http-spray-json" % akkaHttpVersion
 ).map(_ % Provided)
 
-val curatorVersion = "2.12.0"
+val curatorVersion = "4.2.0"
 
 val zkDependencies = Seq(
   "curator-framework",
@@ -39,7 +39,7 @@ val testDependencies = Seq(
   "com.typesafe.akka" %% "akka-testkit" % akkaVersion,
   "com.typesafe.akka" %% "akka-actor" % akkaVersion,
   "com.typesafe.akka" %% "akka-cluster" % akkaVersion,
-  "org.scalatest" %% "scalatest" % "3.0.1",
+  "org.scalatest" %% "scalatest" % "3.0.8",
   "com.typesafe.akka" %% "akka-multi-node-testkit" % akkaVersion,
   "com.typesafe.akka" %% "akka-slf4j" % akkaVersion,
   "org.slf4j" % "log4j-over-slf4j" % "1.7.7",
diff --git a/src/main/scala/akka/cluster/seed/ExhibitorClient.scala b/src/main/scala/akka/cluster/seed/ExhibitorClient.scala
index cfa199c..4af809b 100644
--- a/src/main/scala/akka/cluster/seed/ExhibitorClient.scala
+++ b/src/main/scala/akka/cluster/seed/ExhibitorClient.scala
@@ -2,7 +2,6 @@ package akka.cluster.seed
 
 import java.security.cert.X509Certificate
 import javax.net.ssl.{SSLContext, X509TrustManager}
-
 import akka.actor.ActorSystem
 import akka.http.scaladsl._
 import akka.http.scaladsl.model.Uri.Path
@@ -12,10 +11,8 @@ import akka.util.{ByteString, Timeout}
 import com.typesafe.sslconfig.akka.AkkaSSLConfig
 import spray.json.DefaultJsonProtocol._
 import spray.json.JsonParser
-
 import scala.concurrent.duration._
 import scala.concurrent.{ExecutionContext, ExecutionContextExecutor, Future}
-import scala.language.postfixOps
 
 case class ExhibitorClient(system: ActorSystem, exhibitorUrl: String, requestPath: String, validateCerts: Boolean) extends Client {
 
@@ -75,9 +72,9 @@ object SSL {
 
   lazy val nonValidatingContext: SSLContext = {
     class IgnoreX509TrustManager extends X509TrustManager {
-      def checkClientTrusted(chain: Array[X509Certificate], authType: String) {}
+      def checkClientTrusted(chain: Array[X509Certificate], authType: String):Unit = {}
 
-      def checkServerTrusted(chain: Array[X509Certificate], authType: String) {}
+      def checkServerTrusted(chain: Array[X509Certificate], authType: String): Unit = {}
 
       def getAcceptedIssuers = null
     }
diff --git a/src/main/scala/akka/cluster/seed/ZookeeperClusterSeed.scala b/src/main/scala/akka/cluster/seed/ZookeeperClusterSeed.scala
index 9d8d23b..4be8622 100644
--- a/src/main/scala/akka/cluster/seed/ZookeeperClusterSeed.scala
+++ b/src/main/scala/akka/cluster/seed/ZookeeperClusterSeed.scala
@@ -1,7 +1,6 @@
 package akka.cluster.seed
 
 import java.io.Closeable
-
 import akka.actor._
 import akka.cluster.{AkkaCuratorClient, AutoDownUnresolvedStrategies, Cluster, ZookeeperClusterSeedSettings}
 import org.apache.curator.framework.CuratorFramework
@@ -9,7 +8,6 @@ import org.apache.curator.framework.recipes.cache.{PathChildrenCache, PathChildr
 import org.apache.curator.framework.recipes.leader.{LeaderLatch, LeaderLatchListener}
 import org.apache.curator.framework.state.{ConnectionState, ConnectionStateListener}
 import org.apache.zookeeper.KeeperException.{NoNodeException, NodeExistsException}
-
 import scala.annotation.tailrec
 import scala.collection.JavaConverters._
 import scala.collection.{immutable, mutable}
@@ -102,11 +100,11 @@ class ZookeeperClusterSeed(system: ExtendedActorSystem) extends Extension {
     def waitForLeaderChange(times: Int, delay: Int)
                            (removedAddress: String): Either[Unit, Unit] =
       latch.getLeader.getId.equals(removedAddress) match {
-        case false => Left(null)
+        case false => Left(())
         case _ if times > 0 =>
           Thread.sleep(delay)
           waitForLeaderChange(times - 1, delay)(removedAddress)
-        case _ => Right(null)
+        case _ => Right(())
       }
 
     val pathCache = new PathChildrenCache(client, path, true)
@@ -206,7 +204,7 @@ class ZookeeperClusterSeed(system: ExtendedActorSystem) extends Extension {
     }
   }
 
-  private def createPathIfNeeded() {
+  private def createPathIfNeeded(): Unit = {
     Option(client.checkExists().forPath(path)).getOrElse {
       try {
         client.create().creatingParentsIfNeeded().forPath(path)