Update gatsby-style-guide.md

[jaronheard]

Description

Changes link to Hemingway App from https://www.hemingwayapp.com/ to https://hemingwayapp.com/ because https://www.hemingwayapp.com/ has an invalid SSL certificate and is flagged as a security risk.

Related Issues

[sidharthachatterjee]

It seems to redirect correctly in Chrome but I do see the security risk warning in Safari so I suppose there's no harm in updating this 🙂

Thanks!

[gatsbot]

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