Fix segment.io addon pom file

The segment.io addon has had trouble being released by the IT-release-on-demand addon.

1. project tag in parent pom was missing namespaces (see NXP-14209), fixed by the following commits:
(master) https://github.com/nuxeo/nuxeo-segment.io-connector/commit/f07293d2c7015d0e90d0c7f1c0bc35737e5cfb01
(5.7.1) https://github.com/nuxeo/nuxeo-segment.io-connector/commit/b0425fa84cc00ee389652b4b877a4d8a9649fe56

Both commits introduced a typo (duplicate ">" char) that made jenkins jobs fail:

http://qa.nuxeo.org/jenkins/view/All/job/nuxeo-segment.io-connector-5.7/4
http://qa.nuxeo.org/jenkins/view/All/job/nuxeo-segment.io-connector-master/4/

2. deployment of the 5.7.1 release was still done by the IT-release-on-demand-addon job (for Connect, see NXCONNECT-609) was done in a wrong repository (nightly-staging instead of public-releases) and tag was not pushed (http://qa.nuxeo.org/jenkins/job/IT-release-on-demand-addon/224/) --> maybe this is linked to changes for NXP-13826

--> should have checked "no staging", executing the "perform" task should fix this