added tycho version to pom

Change-Id: I9a460e380fb39c7bbf3cc191b24d7fcd2873d707
diff --git a/releng/org.eclipse.ease.releng/hudson/master.pom.xml b/releng/org.eclipse.ease.releng/hudson/master.pom.xml
index ac3d62b..6b74395 100644
--- a/releng/org.eclipse.ease.releng/hudson/master.pom.xml
+++ b/releng/org.eclipse.ease.releng/hudson/master.pom.xml
@@ -9,6 +9,12 @@
 	<name>EASE</name>
 	<packaging>pom</packaging>
 
+	<properties>
+		<!-- used plugin versions -->
+		<tycho.version>0.21.0</tycho.version>
+		<tycho.extras.version>${tycho.version}</tycho.extras.version>
+	</properties>
+
 	<modules>
 		<module>ease.core</module>
 		<module>ease.modules</module>
@@ -43,7 +49,7 @@
 					<plugin>
 						<artifactId>tycho-p2-extras-plugin</artifactId>
 						<groupId>org.eclipse.tycho.extras</groupId>
-						<version>${tycho.version}</version>
+						<version>${tycho.extras.version}</version>
 						<executions>
 							<execution>
 								<id>addModules</id>