Ensure Hazelcast 4 compatibility with Java 9+

Author: eleftherias

spring-session-hazelcast/hazelcast4/hazelcast4.gradle

@@ -23,6 +23,7 @@ dependencies {
     compile project(':spring-session-core')
     compile "com.hazelcast:hazelcast:4.0.2"
     compile "org.springframework:spring-context"
+    compile "javax.annotation:javax.annotation-api"
 
     testCompile "javax.servlet:javax.servlet-api"
     testCompile "org.springframework:spring-web"