Custom Loader is not asked for HTTP $refs

[YStrauch]

1. What version of the module is the issue happening on? Does the issue happen on latest version?
   Version 0.3.5 (current)

2. What platform and Node.js version? (For example Node.js 0.12 on Mac OS X)
   Node 6.9 OSX

3. Sample source code or steps to reproduce

{
  "description": "Just some JSON schema.",
  "title": "Basic Widget",
  "type": "object",
  "properties": {
    "foo": {
      "$ref": "http://www.mysite.com/myschema.yaml#/definitions/foo"
    }
  }
}

I need to support yaml files, so I wrote a custom loader that will parse yaml files, which is working well when I work locally. However when the yaml file is loaded via internet my custom loader is not called.

I'd expect the custom loader to be called the same way as if the $ref was pointing to a local file.