[Snyk] Security upgrade gatsby from 4.14.0 to 4.25.2

Snyk has created this PR to fix one or more vulnerable packages in the `yarn` dependencies of this project.

Changes included in this PR

Changes to the following files to upgrade the vulnerable dependencies to a fixed version:
- package.json
- yarn.lock

Note for zero-installs users

If you are using the Yarn feature zero-installs that was introduced in Yarn V2, note that this PR does not update the .yarn/cache/ directory meaning this code cannot be pulled and immediately developed on as one would expect for a zero-install project - you will need to run yarn to update the contents of the ./yarn/cache directory. If you are not using zero-install you can ignore this as your flow should likely be unchanged.

Vulnerabilities that will be fixed

With an upgrade:

Severity	Priority Score (*)	Issue	Breaking Change	Exploit Maturity
	768/1000 Why? Proof of Concept exploit, Recently disclosed, Has a fix available, CVSS 7.5	Uncaught Exception SNYK-JS-YAML-5458867	No	Proof of Concept

(*) Note that the real score may have changed since the PR was raised.

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darrenbritton / darrenbritton.github.io