Fixes for virtus 1.0 compatibility

The arity of Virtus::Attribute.build changed. It no longer takes a name
as the first argument. Also it appears like there may be a bug with
coercion using [Virtus::Attributes::Boolean].

Looks like it is getting resolved here:
https://github.com/solnic/virtus/issues/204

May be able to roll back some of this shortly
Looks like string can be used in the interim
extract method to help document param validations