title: Dialogflow not detecting Line location message
body: <p>I am struggling with Line location message.<br>
  My webhook is sending the action button to prompt the user with the location sharing view and then the location is sent back (theoretically) to Dialogflow and then to the webhook.<br>
  But the location message, when sent back, is never detected/interpreted by Dialogflow nor the webhook.<br>
  I don’t see anything happening on both sides, as if the message was never send.</p>
  
  <p>Location message send from the webhook to give the user the possibility to send back he’s location :</p>
  
  <pre><code>{
    "line": {
      "type": "template",
      "altText": "this is a buttons template",
      "template": {
        "type": "buttons",
        "thumbnailImageUrl": "https://example.com/bot/images/image.jpg",
        "title": "Menu",
        "text": "Please select",
        "actions": [
          {
            "type": "uri",
            "label": "View detail",
            "uri": "line://nv/location"
          }
        ]
      }
    }
  }
  </code></pre>
  
  <p>As mentioned in Line’s Messaging API Reference the location message send from the user should look like this :</p>
  
  <pre><code>{
      "type": "location",
      "title": "my location",
      "address": "〒150-0002 東京都渋谷区渋谷２丁目２１−１",
      "latitude": 35.65910807942215,
      "longitude": 139.70372892916203
  }
  </code></pre>
  
  <p>I don’t understand why nothing is happening, if someone as an idea, please help me.<br>
  Thanks !</p>