Use the Travis' Trusty build environment
Use the Travis' Trusty build environment

To see if that solves the XML validation issues (since the issues are
possibly happening due to old libxml versions).

bigfoot90/doctrine2,Ocramius/doctrine2,tPl0ch/doctrine2,bigfoot90/doctrine2,stof/doctrine2,localheinz/doctrine2,Ocramius/doctrine2,doctrine/doctrine2,tPl0ch/doctrine2,TomasVotruba/doctrine2,aivus/doctrine2,holtkamp/doctrine2,gencer/doctrine2,Sitetheory/doctrine2,lcobucci/doctrine2,TomasVotruba/doctrine2,PowerKiKi/doctrine2,Ocramius/doctrine2,lcobucci/doctrine2,deeky666/doctrine2,mikeSimonson/doctrine2,Sitetheory/doctrine2,localheinz/doctrine2,Majkl578/doctrine2,gencer/doctrine2,stof/doctrine2,deeky666/doctrine2,PowerKiKi/doctrine2,holtkamp/doctrine2,aivus/doctrine2,mikeSimonson/doctrine2,doctrine/doctrine2,Majkl578/doctrine2