React-jsonschema-form: Error LIs should be in a UL

[magopian]

Prerequisites

• [x] I have read the documentation.
  

  Description

When a form field displays an error, it's in a li tag, which isn't in an ul tag.

Steps to Reproduce

1. Go to http://mozilla-services.github.io/react-jsonschema-form/ on the "errors" tab
2. check the errors (for example on the "first name" field)
3. see that there's li that are in a div without a ul
   

   Expected behavior

A li item should be in a ul tag.

Actual behavior

The li tags aren't in a ul tag.

Version

0.19.2

[magopian]

I approve this issue template.