Server with relative location are not converted to an absolute url

[jmini]

The OAS3 spec specifies:

This URL supports Server Variables and MAY be relative, to indicate that the host location is relative to the location where the OpenAPI document is being served.

With a server that serves on http://localhost:8090/openapi.json:

{
  "openapi": "3.0.1",
  "servers": [
    {
      "url": "/rel"
    }
  ],
  "info": {
    "description": "This is a sample server",
    "version": "1.0.0",
    "title": "OpenAPI Petstore",
    "license": {
      "name": "Apache-2.0",
      "url": "http://www.apache.org/licenses/LICENSE-2.0.html"
    }
  },
  "paths": {
    "/ping": {
      "get": {
        "summary": "Some ping operation",
        "description": "Some ping operation",
        "operationId": "doPing",
        "responses": {
          "200": {
            "description": "OK",
            "content" : {
              "application/json" : {
                "schema" : {
                  "type" : "object",
                  "properties" : {
                    "status": {
                      "type" : "string",
                      "example" : "ok",
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

When you do:

String inputSpec = "http://localhost:8090/openapi.json";

OpenAPIParser openApiParser = new OpenAPIParser();
ParseOptions options = new ParseOptions();
options.setResolve(true);
options.setFlatten(true);

System.out.println(openAPI.getServers().get(0).getUrl()); //should be http://localhost:8090/rel

You get /rel where the expected value is http://localhost:8090/rel

---

Tested with:

<groupId>io.swagger.parser.v3</groupId>
<artifactId>swagger-parser</artifactId>
<version>2.0.1</version>

[jmini]

Solved with merge of #773