Add support for npm package aliases

[Cherry]

npm 6.9.0 added support for aliasing packages in your package.json, so for example, you could install postman-request, but into the request folder as per the syntax below:

"request": "npm:postman-request@2.88.1-postman.16"

More references:

• https://github.com/npm/rfcs/blob/latest/implemented/0001-package-aliases.md
• npm/cli@b7b54f2
• install: add support for package aliases npm/cli#3

As per the example above, I'm using postman-request@2.88.1-postman.16 which is out of date, but not being detected by ncu. The latest version at time of writing as per https://www.npmjs.com/package/postman-request, is 2.88.1-postman.19.

There's a lot of use-cases for this, but one of the more common ones is actually as I'm describing above - migrating off of an older unmaintained library to another one with an identical API, without making too many code changes. It would be great to see this syntax supported in npm-check-updates.

[raineorshine]

Great suggestion. I'm happy to support and provide guidance for a PR for this feature.

[raineorshine]

@Cherry @l5x I attempted a fix in #715. Could you try npm install -g npm-check-updates@7.0.5-alpha.1 and see if it works for you?

[Cherry]

@raineorshine Awesome! From some basic testing, things seem to work as I'd expect when using a package alias! Thanks for the feature addition!

[raineorshine]

Great, thank you!

I will merge into master and publish to latest once #716 is tested more, since they both entail a major version bump.