pom.xml: updates for release 0.50
pom.xml: updates for release 0.50

shopping cart API
Add START_OF_TERM BillingActionPolicy

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

killbill/killbill-api,killbill/killbill-api