Dependency Upgrade bump Express from 4.20.0 to 4.21.2

[hexaltation]

Context

Follow-up of #1368

Express 4.2.0 have some known dependency vulnerabilities.
This PR addresses it.

Proposed solution

Bump express from 4.20.0 to 4.21.2

• Releases
• Commits

Fix /boot/key route

A routing fix for /boot was necessary to workaround new version of path-to-regex

Previous route handling for /boot/KEY was crashing after express update

SyntaxError: Invalid regular expression: /^/boot(/(?:(?:((?:(?!/|/boot(/).)+?))/?)?)?$/?$/i: Unterminated group
    at new RegExp (<anonymous>)
    at pathToRegexp (/home/hexa/Programmation/DINUM/grist-core/node_modules/path-to-regexp/index.js:155:10)
    at new Layer (/home/hexa/Programmation/DINUM/grist-core/node_modules/express/lib/router/layer.js:45:17)
    at Function.route (/home/hexa/Programmation/DINUM/grist-core/node_modules/express/lib/router/index.js:505:15)
    at app.<computed> [as get] (/home/hexa/Programmation/DINUM/grist-core/node_modules/express/lib/application.js:498:30)
    at FlexServer.addBootPage (/home/hexa/Programmation/DINUM/grist-core/_build/app/server/lib/FlexServer.js:519:18)
    at MergedServer.create (/home/hexa/Programmation/DINUM/grist-core/_build/app/server/MergedServer.js:91:27)
    at async main (/home/hexa/Programmation/DINUM/grist-core/_build/stubs/app/server/server.js:137:26)

So it has been simplified to perform the same with less syntactic complexity.

- '/boot(/(:bootKey/?)?)?$'
+ '/boot(/*)?'

Has this been tested?

• 👍 yes, with this PR CI

[fflorent]

LGTM!