Addex xtend gen folder to src includes

plugins/org.yakindu.sct.model.stext/build.properties

@@ -1,5 +1,6 @@
 source.. = src/,\
-           src-gen/
+           src-gen/,\
+           xtend-gen/
 bin.includes = META-INF/,\
                .,\
                plugin.xml