Fixes to actuator metrics

- Quick fix to get something out from
  new boot 2.x metrics.
- Change source to java 8 compat
- Add new micrometer deps to build
- Docs and further changes will get done
  when new boot metric system completes.
- Fixes #410

spring-statemachine-samples/web/src/main/java/demo/web/WebSocketConfig.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 the original author or authors.
+ * Copyright 2015-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package demo.web;
 
+import java.util.concurrent.ConcurrentHashMap;
+
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.messaging.simp.config.MessageBrokerRegistry;
@@ -41,7 +43,7 @@ public class WebSocketConfig extends AbstractSessionWebSocketMessageBrokerConfig
 
 	@Bean
 	public MapSessionRepository mapSessionRepository() {
-		return new MapSessionRepository();
+		return new MapSessionRepository(new ConcurrentHashMap<>());
 	}
 
 }