title: Displaying Image in Image Attachment
body: <p>According to the Slack API, if you provide a valid link to an image_url, that image will be displayed. I've tried this with the message builder <a href="https://api.slack.com/docs/messages/builder?msg=%7B%22attachments%22%3A%5B%7B%22fallback%22%3A%22Required%20plain-text%20summary%20of%20the%20attachment.%22%2C%22text%22%3A%22Optional%20text%20that%20appears%20within%20the%20attachment%22%2C%22image_url%22%3A%22https%3A%2F%2Fimgur.com%2Fa%2FxVS7Qgv%22%2C%22thumb_url%22%3A%22https%3A%2F%2Fimgur.com%2Fa%2FxVS7Qgv%22%7D%5D%7D" rel="nofollow noreferrer">here</a> but no image is ever displayed. I also tried this using cURL, and once again the image doesn't display. Any idea how to get the image to display? This is for use in creating a bot to send notifications through an incoming webhook. Thanks!</p>
  
  <p>Image of JSON and corresponding message preview:</p>
  
  <p><img src="https://i.stack.imgur.com/7yV9v.png" alt="Image of JSON and corresponding message preview"></p>