fixed missing file reference for the version 5.0

Signed-off-by: Florian Thienel <florian@thienel.org>
diff --git a/org.eclipse.vex.docbook/build.properties b/org.eclipse.vex.docbook/build.properties
index 25ee170..17df738 100644
--- a/org.eclipse.vex.docbook/build.properties
+++ b/org.eclipse.vex.docbook/build.properties
@@ -3,7 +3,8 @@
                .,\
                plugin.properties,\
                META-INF/,\
-               4.5/
+               4.5/,\
+               5.0/
                
 src.includes = styles/,\
                4.5/