fix: upgrade gatsby from 5.12.4 to 5.13.4

Snyk has created this PR to upgrade gatsby from 5.12.4 to 5.13.4.

See this package in npm:
https://www.npmjs.com/package/gatsby

See this project in Snyk:
https://app.snyk.io/org/sammyfilly/project/e8b4c65c-60ed-47ef-b727-c02554fe6f00?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot