Make CONTEXTUAL_DATA_KEY constant

It shouldn't be allowed to change it.

Author: tsegismont

hibernate-reactive-core/src/main/java/org/hibernate/reactive/context/impl/ContextualDataStorage.java

@@ -17,7 +17,7 @@
 public class ContextualDataStorage implements VertxServiceProvider {
 
 	@SuppressWarnings("rawtypes")
-	static ContextLocal<ConcurrentMap> CONTEXTUAL_DATA_KEY = ContextLocal.registerLocal( ConcurrentMap.class );
+	final static ContextLocal<ConcurrentMap> CONTEXTUAL_DATA_KEY = ContextLocal.registerLocal( ConcurrentMap.class );
 
 	@Override
 	public void init(VertxBuilder vertxBuilder) {