Set Xtend compiler version to 2.8.3

releng/org.yakindu.sct.releng/pom.xml

@@ -241,7 +241,7 @@
 				<plugin>
 					<groupId>org.eclipse.xtend</groupId>
 					<artifactId>xtend-maven-plugin</artifactId>
-					<version>2.7.2</version>
+					<version>2.8.3</version>
 					<configuration>
 						<!-- need to prefix by basedir to generate to currently built module -->
 						<outputDirectory>${basedir}/xtend-gen</outputDirectory>