Set up deploy keys

[zakhenry]

See https://developer.github.com/guides/managing-deploy-keys/

Deploy keys allow single repo access to publish, so in this case a new key should be created, assigned to this repo and updated in the encrypted file at ubiquits/core/.travis/deploy_key.pem.enc This way there is minimal risk of damage as the key will only have rights to this (basically throwaway) repo.