fix: upgrade gatsby from 5.0.0 to 5.12.3

Snyk has created this PR to upgrade gatsby from 5.0.0 to 5.12.3.

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

See this project in Snyk:
https://app.snyk.io/org/sammyfilly/project/af737f69-1615-4ff8-88ef-8864ae118b27?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot