Fix for relative ref with fragment identifier on Windows

Schemas like this won't work on Windows:

```json
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "properties": {
    "a": {
      "$ref": "definition_schema.json#/definitions/foo"
    }
  }
}
```
Relative links always have # [appended](https://github.com/arcticlcc/json-schema/blob/chomp/lib/json-schema/validator.rb#L261). From what I can tell, since the path isn't [in the format *xxx://*](https://github.com/ruby/ruby/blob/trunk/lib/open-uri.rb#L17), it's passed on to *Kernel#open* as is - with the trailing #.

Adding chomp('#') fixes the issues. I don't see any problems causes by the addition. All tests pass(new ones added to test for relative refs with fragments) on Win and Linux.