Make `developer` a required field (bug 875344)
Make `developer` a required field (bug 875344)

I'm being lazy and not testing err.hosted because nobody uses it.
eviljeff/app-validator,stasm/app-validator,mstriemer/app-validator,mozilla/app-validator,mozilla/app-validator,stasm/app-validator,diox/app-validator,stasm/app-validator,mstriemer/app-validator,diox/app-validator,stasm/app-validator,mozilla/app-validator,mstriemer/app-validator,diox/app-validator,eviljeff/app-validator,eviljeff/app-validator,diox/app-validator,mozilla/app-validator,eviljeff/app-validator