pom.xml: updates for release 0.141.62
pom.xml: updates for release 0.141.62

Update killbill-api -> 0.51.18 and killbill-client -> 0.41.12

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

killbill/killbill-oss-parent