build: Upgrade Node.js to a supported version

[stephenmathieson]

This patch updates the version of Node.js used for development. Prior to this, the version specified was neither compatible with our dependencies nor supported.

➜  cauldron git:(develop) nvm use
Found '/Users/stephen/dev/src/github.com/dequelabs/cauldron/.nvmrc' with version <14>
Now using node v14.21.0 (npm v6.14.17)
➜  cauldron git:(develop) yarn
yarn install v1.22.19
warning ../package.json: No license field
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
error @playwright/experimental-ct-react17@1.48.1: The engine "node" is incompatible with this module. Expected version ">=18". Got "14.21.0"
error Found incompatible module.
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
➜  cauldron git:(develop)

No QA required.