Description must follow Format version

[lrworth]

This seems inconsequential but I feel it needs to be mentioned somewhere:

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-anatomy.html under "Description" states that "This section must always follow the template format version section." (For searchability: Description must always follow AWSTemplateFormatVersion).

Currently dhallToYaml generates keys in alphabetical order (I don't understand how), which luckily orders those keys correctly. If this were to ever change it could result in malformed cloudformation templates. It'd be nice to safeguard against that somehow.