[pub] Use official version endpoint for pub-service

[sigurdm]

• pub.dartlang.org is replaced by pub.dev as the official pub site.
• api/packages/<packageName> is the official endpoint for retrieving a version listing.
  see https://pub.dev/help/api#hosted-pub-repository-api -> https:/dart-lang/pub/blob/master/doc/repository-spec-v2.md#list-all-versions-of-a-package

The packages/<packageName>.json endpoint is obsolete and might go away.

[github-actions]

	Warnings
⚠️	This PR modified service code for pub but not its test code. That's okay so long as it's refactoring existing code.

	Messages
📖	✨ Thanks for your contribution to Shields, @sigurdm!

Generated by 🚫 dangerJS against 4da8f3f

[chris48s]

Thanks. The reason the tests are failing is because we also need to update the schema to account for the new response format:

shields/services/pub/pub.service.js

Lines 6 to 8 in 78f8324

	const schema = Joi.object({
	versions: Joi.array().items(Joi.string()).required(),
	}).required()

At the moment we're rejecting the API responses because they don't match the schema. Could you update?

[sigurdm]

At the moment we're rejecting the API responses because they don't match the schema. Could you update?

Ah of course

Done!

[chris48s]

I pushed one last edit as it was easier than another round of back-and-forth.
Merging - thanks 👍