tinacms breaks if the site using it has a different version of styled-componentst

[ncphillips]

Description

A user reported in #356 that their site did not work with tinacms.

The site is using [email protected]

TinaCMS uses [email protected]

After upgrading the site's version of styled-components to 4.3.2 everything worked fine locally, although it may not have fixed everything in production.

Steps to reproduce

• Add gatsby-plugin-tinacms to a gatsby site using a version of styled-components other than 4.3.2.
• Run gatsby develop
• Open browser and see errors

Expected result

Tina works fine

Actual result

Tina explodes