Rename publishTo resolvers to something less common

[listba]

per #22 it appears that if a user adds a resolver with the name gitlab-maven it overrides the publishTo resolver added by the plugin, and thus breaks publishing. Since this seems like a name that would be pretty easy for a user to default to when adding a group level gitlab resolver, I think it makes sense to name the one generated by the plugin to something a bit more unique like gilcloud-sbt-gitlab-maven