Update init.sls

there is difference between  http://yum.opengeo.org/centos/6/x86_64/OpenGeo.repo and http://yum.opengeo.org/centos/5/x86_64/OpenGeo.repo, also the value of md5 is belong to http://yum.opengeo.org/centos/6/x86_64/OpenGeo.repo.