toOptional not working with a nested case class

[pinguinson]

Seems to be related related to #43
Tested with version 0.6.2
This snippet:

import henkan.optional.all._

object HenkanTest extends App {

  case class Foo(value: String)
  case class Domain(foo: Foo)
  case class Message(foo: Option[Foo])

  val dom = Domain(Foo("123"))
  val msg = Message(Some(Foo("123")))
  validate(msg).to[Domain] // works
  from(dom).toOptional[Message] // fails to compile

}

Results in the following error messages:

Error:(14, 23) Cannot build toOptional conversion from HenkanTest.Domain to HenkanTest.Message, possibly due to missing cats instances (`Functor` instances are needed to convert fields in containers)
  from(dom).toOptional[Message] // fails to compile
Error:(14, 23) not enough arguments for method toOptional: (implicit t: henkan.optional.ToOptional[HenkanTest.Domain,HenkanTest.Message])HenkanTest.Message.
Unspecified value parameter t.
  from(dom).toOptional[Message] // fails to compile

[pinguinson]

Would gladly look into the issue myself, but my understanding of shapeless leaves a lot to be desired.

P.S. We're using henkan in production, your library is an absolute lifesaver!

[kailuowang]

fixed with release 0.6.3. please verify and feel free to close this one.

[pinguinson]

Works like a charm, thanks! Closing the issue