title: MalformedURLException when using "$ref" in json schema
body: <p>I have a json schema which refers to another json schema present in another folder using "$ref" (relative path) and i get a "MalformedURLException".</p>
  
  <pre><code>{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "$ref": "#/definitions/Base",
    "definitions": {
      "Base": {
        "type": "object",
        "additionalProperties": false,
        "properties": {
          "event": {
            "$ref": "com/artifacts/click/ClickSchema.json"
          },
          "arrival_timestamp": {
            "type": "integer",
            "minimum": 0.0
          }
        },
        "title": "Base"
      }
    }
  }
  </code></pre>
  
  <p>And the click schema in another folder is as follows:</p>
  
  <pre><code>{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "$id": "com/artifacts/click/ClickSchema.json",
    "Event": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "sourceName": {
          "type": "string"
        }
      }
    }
  }
  </code></pre>
  
  <p>Can someone please help. I am using <a href="https://github.com/everit-org/json-schema" rel="nofollow noreferrer">this</a> schema validator.</p>