fix: upgrade gatsby-plugin-image from 3.0.0 to 3.12.3

Snyk has created this PR to upgrade gatsby-plugin-image from 3.0.0 to 3.12.3.

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

See this project in Snyk:
https://app.snyk.io/org/sammyfilly/project/c2ba23e1-8e78-4d98-a602-4215c0203b4d?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot