Update PekkoHttpTestWebServer.scala

Author: pjfanning

instrumentation/pekko/pekko-http-1.0/javaagent/src/test/scala/io/opentelemetry/javaagent/instrumentation/pekkohttp/v1_0/PekkoHttpTestWebServer.scala

@@ -19,7 +19,7 @@ import scala.concurrent.{Await, ExecutionContext}
 
 object PekkoHttpTestWebServer {
   implicit val system: ActorSystem = ActorSystem("my-system")
-  implicit val materializer = ActorMaterializer()
+  implicit val materializer: ActorMaterializer = ActorMaterializer()
   // needed for the future flatMap/onComplete in the end
   implicit val executionContext: ExecutionContext = system.dispatcher