Added backport-util-concurrent lib

Change-Id: I7140fa961d618ddb5681a4cc26bd2e467148c76d
diff --git a/core/pom.xml b/core/pom.xml
index 7fab757..3303cf8 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -96,6 +96,13 @@
 		</plugins>
 	</build>
 	<dependencies>
+		<!-- backport -->
+		<dependency>
+		    <groupId>backport-util-concurrent</groupId>
+		    <artifactId>backport-util-concurrent</artifactId>
+		    <version>3.1</version>
+		</dependency>
+	
 		<!-- Jersey -->
 		<dependency>
 			<groupId>com.sun.jersey</groupId>