changed property.default to property.defaultValue to match swagger-ui

I'm brand new to using hapi-swagger (and swagger), but so far it looks awesome. I noticed that on the documentation page for my API, there were no default values for parameters, despite the fact that I was providing defaults via joi's .default(). This one liner fixes the problem. I'm not sure if there is a better approach, but I thought I would put this out there for review..