Install guide not working as you can't easily get Node 10

[joelanman]

The docs currently tell people to use Node v10, and point people to https://nodejs.org/en/.

v10 is not easily available there as the new LTS is v12.

[joelanman]

just ran npm run test in Node v12.13.0 and got this (seems to be the important line at the end)

> govuk-prototype-kit@9.3.0 test /Users/joelanman/projects/govuk-prototype-kit
> npm run lint && gulp generate-assets && jest


> govuk-prototype-kit@9.3.0 lint /Users/joelanman/projects/govuk-prototype-kit
> standard

[12:09:57] Using gulpfile ~/projects/govuk-prototype-kit/gulpfile.js
[12:09:57] Starting 'generate-assets'...
[12:09:57] Starting 'clean'...
[12:09:57] Finished 'clean' after 15 ms
[12:09:57] Starting 'sass-extensions'...
[12:09:57] Finished 'sass-extensions' after 1.91 ms
[12:09:57] Starting 'sass'...
[12:09:57] Starting 'copy-assets'...
[12:09:57] Starting 'sass-documentation'...
[12:09:57] Starting 'copy-assets-documentation'...
[12:09:57] Starting 'sass-v6'...
[12:09:57] Starting 'copy-assets-v6'...
[12:09:57] Finished 'sass-v6' after 25 ms
[12:09:57] Finished 'copy-assets-v6' after 26 ms
[12:09:58] Finished 'copy-assets-documentation' after 126 ms
[12:09:58] Finished 'copy-assets' after 177 ms
[12:09:58] Finished 'sass-documentation' after 665 ms
[12:09:58] Finished 'sass' after 970 ms
[12:09:58] Finished 'generate-assets' after 989 ms
 PASS  lib/middleware/authentication/authentication.test.js
 PASS  lib/extensions/extensions.test.js
 PASS  __tests__/spec/force-https-redirect.js
  ● Console

    console.warn node_modules/express-session/index.js:154
      Warning: connect.session() MemoryStore is not
      designed for a production environment, as it will leak
      memory, and will not scale past a single process.
    console.log server.js:341
      
      GOV.UK Prototype Kit v9.3.0
    console.log server.js:342
      
      NOTICE: the kit is for building prototypes, do not use it for production services.
    console.log lib/utils.js:126
      Redirecting request to https
    console.log lib/utils.js:126
      Redirecting request to https
    console.log lib/utils.js:126
      Redirecting request to https

 PASS  __tests__/spec/sanity-checks.js
  ● Console

    console.log server.js:341
      
      GOV.UK Prototype Kit v9.3.0
    console.log server.js:342
      
      NOTICE: the kit is for building prototypes, do not use it for production services.
    console.error server.js:336
      Page not found: /govuk/assets/common.js


Test Suites: 4 passed, 4 total
Tests:       69 passed, 69 total
Snapshots:   0 total
Time:        5.004s, estimated 6s
Ran all test suites.
Jest did not exit one second after the test run has completed.

This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.

[NickColley]

Can confirm that the kit works with 12, but we should bump things properly in guidance and in our process. We may want to consider updating the other repositories to 12 as well.

Ideally we'd set ourselves reminders based on the Node release schedule: https://nodejs.org/en/about/releases/ to do this before users let us know about it.