update poms to use tycho 0.24.0 to fix the CI build

Signed-off-by: Florian Thienel <florian@thienel.org>
diff --git a/org.eclipse.vex.sdk.feature/pom.xml b/org.eclipse.vex.sdk.feature/pom.xml
index 940e358..834f0e2 100644
--- a/org.eclipse.vex.sdk.feature/pom.xml
+++ b/org.eclipse.vex.sdk.feature/pom.xml
@@ -14,11 +14,19 @@
 	</parent>
 
 	<build>
-		<plugins>
+	    <pluginManagement>
+	      <plugins>
+	        <plugin>
+	          <groupId>org.eclipse.tycho.extras</groupId>
+	          <artifactId>tycho-source-feature-plugin</artifactId>
+	          <version>${tycho-extras-version}</version>
+	        </plugin>
+	      </plugins>
+	    </pluginManagement>
+    	<plugins>
 			<plugin>
 				<groupId>org.eclipse.tycho.extras</groupId>
 				<artifactId>tycho-source-feature-plugin</artifactId>
-				<version>${tycho-extras-version}</version>
 				<executions>
 					<execution>
 						<id>source-feature</id>