Found a bug? Please fill out the sections below. 👍

### Issue Summary

A summary of the issue.

### Steps to Reproduce

1. This is the first step
2. This is the second step, etc.

Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?

### Technical details

* Python version: Run `python --version`.
* Django version: Look in your requirements.txt, or run `pip list | grep -i django`.
* Wagtail version: Hover over the Wagtail bird in the admin, or look in the Settings menu, look in your requirements.txt, or run `pip list | grep -i wagtail`.
* Browser version: You can use http://www.whatsmybrowser.org/ to find this out.
