message: add user constants
diff: package design
  import (
  + _ "github.com/cam-inc/dmc/example-go/bridge"
  . "github.com/goadesign/goa/design"
  . "github.com/goadesign/goa/design/apidsl"
  + "github.com/cam-inc/dmc/example-go/bridge"
  )
  // UserMediaType of media type.
  @@ -119,10 +121,18 @@ var _ = Resource("user", func() {
  var UserPayload = Type("UserPayload", func() {
  Member("name", String)
  Member("sex", String, func() {
  - Enum("male", "female")
  + Enum(
  + bridge.UserMale,
  + bridge.UserFemale,
  + )
  })
  Member("blood_type", String, func() {
  - Enum("A", "B", "O", "AB")
  + Enum(
  + bridge.UserBloodTypeA,
  + bridge.UserBloodTypeB,
  + bridge.UserBloodTypeO,
  + bridge.UserBloodTypeAB,
  + )
  })
  Member("birthday", DateTime)
  Member("job", String)
  