Email notifications for annotation replies contain the wrong document title.

### Steps to reproduce
1. Go to: https://via.hypothes.is/http://firstmonday.org/article/view/6360/5460
2. Create an annotation
3. Get someone to reply to your annotation

### Expected behaviour
The email notification has a link to the article that was annotated.

### Actual behaviour
The email notification has a link to some other article but from the same domain firstmonday.org

### Browser/system information
Chrome

### Additional details
It looks like annotations from articles on firstmonday.org are anchored in the wrong articles.
- A page note here appears on a different (digital reading spaces) article http://firstmonday.org/ojs/index.php/fm/article/view/6169/4904
- https://hyp.is/xK3RiNPHTg2eS_5jbpU-tw/firstmonday.org/ojs/index.php/fm/article/view/2484/2199
- https://hyp.is/uD5JJuNLEeaLLWMYkKcWuw/firstmonday.org/article/view/6360/5460
- https://hyp.is/uD5JJuNLEeaLLWMYkKcWuw/firstmonday.org/article/view/6360/5460
- https://via.hypothes.is/http://firstmonday.org/article/view/2762/2504