title: stubby4node comma separated query string implementation issue
body: <p>I have a URL (GET REQUEST) of the following pattern</p>
  <ul>
  <li>^/testpath/1/test?pathid=1</li>
  <li>^/testpath/1/test?pathid=1,2</li>
  <li>^/testpath/1/test?pathid=1,2,5</li>
  </ul>
  <p>where pathid query string parameters are comma separated</p>
  <p>I have the following stubby mappings to match these url patterns</p>
  <pre><code>- request:
      url: ^/testpath/(.*)/test
      query:
        pathid: '1'
      method: GET
    response:
      headers:
        Content-Type: application/json
      status: 200
      file: response/path-1.json
  
  - request:
      url: ^/testpath/(.*)/test
      query:
        pathid: '1,2'
      method: GET
    response:
      headers:
        Content-Type: application/json
      status: 200
      file: response/path-2.json
  
  - request:
      url: ^/testpath/(.*)/test
      query:
        pathid: '1,2,5'
      method: GET
    response:
      headers:
        Content-Type: application/json
      status: 200
      file: response/path-3.json
  </code></pre>
  <p>but I can't get this URL mapping to properly deliver different payloads based on different parameter combinations.</p>
  <ul>
  <li>1 -&gt; payload1</li>
  <li>1,2 -&gt; payload2</li>
  <li>1,2,5 -&gt; payload3</li>
  </ul>
  <p>how can this be done?</p>