pom.xml: updates for release 0.40.4
pom.xml: updates for release 0.40.4

 Add custom field apis for Subscription and Bundles

Signed-off-by: Kill Bill core team <1a73af9e7ae00182733b2292511b814be66f065f@killbill.io>

killbill/killbill-client-java,killbill/killbill-client-java