Update minimum required node.js version to v12 with npm package dependencies

Looks like the node.js and npm dependencies didn't get update for a while, node.js v10 is EoL at 2021-04-30, and there could be a lot of security vulnerabilities since the last release, especially for those using pre-built Docker image on Docker Hub.

The idea here, is try to increase the baseline of the node.js and npm packages "a little bit", and ideally will update to node.js v18, because both of node.js v14 & v16 will reach EoL this year, node.js v12 is EoL at 2022-04-30 last year.

As I can't guarantee how much I can contribute, each PR won't be large, so that we can get it reviewed and merged in a more agile way ;)

Currently, npm run test is the assurance of the update not breaking things, please let me know if that's not enough. Thanks.

Reference:

Prompt message from npm install before the update:

found 350 vulnerabilities (13 low, 163 moderate, 138 high, 36 critical)
Prompt message from npm install after the update:

found 123 vulnerabilities (13 low, 42 moderate, 52 high, 16 critical)

hackmdio / codimd

Update minimum required node.js version to v12 with npm package dependencies #1799