add missing copyright

Author: ghillairet

emfjson-core/src/main/java/org/emfjson/common/ReferenceEntries.java

@@ -1,3 +1,14 @@
+/*
+ * Copyright (c) 2015 Guillaume Hillairet.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     Guillaume Hillairet - initial API and implementation
+ *
+ */
 package org.emfjson.common;
 
 import org.eclipse.emf.ecore.EObject;