Simplify package.json inference

Following up on https://github.com/electron-userland/electron-packager/pull/449#issuecomment-240865736

Currently there’s a bit of code in index.js that uses get-package-info to look for package.json files from which to infer default values for electron version, product name, etc. This technique of recursing up directories can produce unpredictable results depending on the directory structure of a given user.

As @malept said:

Not that I want to drag this PR out any longer, but should we have a test for the case where no app-version is specified and (for some reason) there is no version in any of the package.json files found?

Looking for the first parent package.json file instead of all parent package.json files will enable us to reliably test that scenario. Writing up this issue because I came across a battle-tested package that does what we want: https://www.npmjs.com/package/find-root

[rahatarmanahmed]

Ok, published 1.0.0 of get-package-info, which now returns a better error that lets us know when props can’t be found.

From the README:

If all the properties cannot be found in parent package.json files, then getPackageInfo() will reject it’s promise (or callback with err argument) with an Error. err.missingProps will have an array of the properties that it could not find, and err.result will contain all the props that were found.

If any other error occurs(like I/O or runtime errors), getPackageInfo() will reject with that error itself.

I’ll work on a PR using this new info later tonight.

[malept]

There have been a couple of pull requests that make adding electron (FKA electron-prebuilt) not required to be set in dependencies or devDependencies, nor set via --version (although no one’s actually finished any of the PRs). I’m a bit conflicted about whether that is a good default. Offhand, it seems dangerous, given that basically defaults the dependency to "electron": "*".