Second level of ref object not parsing correctly

[gustavorodrig]

Swagger parser doesn't parse correctly many levels of references when in the second reference are an object that is referencing another file

Imagine this scenario:

`
Main.yaml:

Mail:
type: object
properties:
message:
$ref: "../files/Definitions.yaml#/definitions/Message"

---

Definitions.yaml:

Message:
type: object
properties:
content:
type: object
properties:
contentMessage:
$ref: "../files/others.yaml#/Content"

---

Others.yaml:

Content:
type: object
properties:
text:
type: string
`

In this scenario swagger creates a POJO (ContentMessage) withou any properties and dont create the last object (Content)

I added some code to consider this situation and i will do a pull request.