Update Gatsby dependencies for Gatsby 4

[thinkybeast]

Hi! In case you didn’t know, Gatsby is planning its next major version for Q4 of this year! In preparation, the Gatsby team is reaching out to maintainers for our most popular Starters to help make the upgrade to Gatsby 4 as smooth as possible.

This PR updates this Gatsby Starter to the alpha version of this next release, as well as some related plugins. It’s just in draft form for now, since the 4.0.0 version of Gatsby isn’t quite ready for release yet. We’re mainly testing updating Gatsby and the other official plugins to ensure that the Starter builds without errors.

When running the build, you may see some warnings from packages that list gatsby: ^3.0.0 as a peer dependency. Don’t worry, we’ll come back and fix those before we take this PR out of draft mode when it’s ready to be merged.

• Note: Gatsby 4 requires Node v14. This is a change from Gatsby 3, which worked with Node v12.13 or newer.

Once version 4.0.0 is ready, we'll come back to update the dependencies and convert this draft to a PR for review. Until then, no action is required on your end. If you have any questions / concerns, let us know in the comments.

Thanks again for all your work as a Gatsby maintainer. We’re so grateful to have you as part of our community. 💜

For more information on what’s coming with Gatsby v4, check out the GitHub Discussion.

[thinkybeast]

Gatsby 4 goes GA today! I've updated the dependencies one more time. If everything looks good, feel free to merge this!

[rmatambo8]

Hey @jeremylynch, We just wanted to let you know that we will be removing any starters that are not on Gatsby v4 from our starters library within the next 24 hours.

We would like to keep featuring your starter so if you upgrade to gatsby v4, you can send us a message here and we will add it back to the starters library