feat(v2): notify users when docusaurus version is outdated

[teikjun]

Motivation

Notify the user when their @docusaurus/core version is outdated.
The interval between notifications is set to one day so that it is not too naggy.
This PR closes #2199.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan (edited)

1. Run yarn install in the root directory
2. Open package.json file in /packages/docusaurus, change line 4 to "version": "2.0.0-alpha.56",
3. Go to the /website directory in your terminal, run yarn start. You should see a notification like the one below!

4. Run yarn start again, there should be no notification this time because the interval is set to one day

Additional Remarks

The notify method of update-notifier does not work directly with our docusaurus command, so the implementation needed to be modified.

[docusaurus-bot]

Deploy preview for docusaurus-2 ready!

Built with commit 4dc8560

https://deploy-preview-3032--docusaurus-2.netlify.app

[slorber]

Hey @teikjun

how do you test this exactly?

"@docusaurus/core": "2.0.0-alpha.57" 

does not exist (bad release)

and

"@docusaurus/core": "2.0.0-alpha.56" 

I get:

[teikjun]

Hi @slorber
Sorry, my previous testing instruction was completely incorrect (I got mixed up), please ignore it.
I ran through the testing process from the start and I've updated the first post with exact instructions for testing.

[slorber]

Thanks @teikjun

It seems to almost work, but not on the 1st run of the update notifier for this package.

You can clear its cache on macos with the following command:

rm -rf ~/.config/configstore/update-notifier-@docusaurus

Can you ensure it works fine on the first run too?

[teikjun]

It works on the first run now! The testing instructions are similar to before :)

[slorber]

thanks!