Upgrade to latest dependencies, closes #25

[vadikmash]

Updated TypeScript, React, Preact and Gatsby to their latest versions.

[iamakulov]

Fixed the build issues!

• The issue you’ve experienced initially:

  

  turned out to be caused by the extra webpack@4 dependency. Gatsby v3 relies on webpack v5, but we had v4 installed as a direct dependency for some reason. Removing that dependency left us with a single webpack version – and fixed the issue.

• I also tuned a couple other dependencies to fix the issues I’ve noticed.

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Is there anything else left to upgrade? Does the site (home page, talk page, article page) look correct? I don’t see any build errors or layout issues left, but I’d appreciate if you could take a second look!

(The only thing I noticed is a warning about these plugins being outdated:

but there’s nothing we can do about that yet. The plugins seem to work nicely and just need to update their peer deps. See https://github.com/itmayziii/gatsby-plugin-no-javascript/issues/26 & https://github.com/d4rekanguok/gatsby-remark-images-anywhere/issues/37.)