Fix deploy env template to use valid ansible vars

[henkler]

When running deploy.sh, ansible fails with an error similar to the following:

failed: [staging.example.com] => (item={u'dest': u'.env', u'src': u'roles/deploy/templates/env.j2', u'name': u'.env config'}) => {"failed": true, "item": {"dest": ".env", "name": ".env config", "src": "roles/deploy/templates/env.j2"}, "msg": "AnsibleUndefinedVariable: 'dict object' has no attribute 'value'"}

It apepars that PR #528 introduced an error with some invalid ansible keys. This should fix them.

Thanks to @fullyint for helping with Ansible conventions. I'm new to Trellis (and Ansible), and you make it easy!

[fullyint]

Thank you @henkler !