Default does not implement MarshalJSON

[asaf]

Environment

What version of qri are you using (qri version)?

0.2.1

Issue

What happened?

The Default is not marshaled properly.
instead of the actual default value, it always yields {}

This is because the Default struct contains a private data which will never get marshalled without a custom MarshalJSON func.

What did you expect to happen?

The actual value to be jsonized.

Please link any related issues.

Do you have a suggested fix?

Yes, creating a PR now.