API: deploy_branch default should depend on deploy_repo not deploy_dir
API: deploy_branch default should depend on deploy_repo not deploy_dir

If we are deploying *to* a github.io repo we must deploy to 'master' (GH does
not even let you configure this -- it's always 'master') regardless of whether
we are publishing content *from* a *.github.io repo or some other repo. Thus,
deploy_repo, not deploy_dir.

drdoctr/doctr