Project root detection differs with pkg#source vs CLI argument

[mischnic]

🐛 bug report

💻 Code Sample

folder-a
|- packages
|  |- pkg-a
|     |- index.js
|     |- package.json
|     |- yarn.lock
|- yarn.lock

package.json contains:

{
	"source": "index.js"
}

😯 Current Behavior

With the working directory at folder-a/packags/pkg-a, running parcel build will correctly bundle index.js, but the project root will be folder-a.

With the working directory at folder-a/packags/pkg-a, running parcel build index.js will correctly bundle index.js and correctly determine the project root to be folder-a/packags/pkg-a

🤔 Expected Behavior

The project root should in both cases be folder-a/packags/pkg-a

🌍 Your Environment

Software	Version(s)
Parcel	f9887fe

[mischnic]

Fixed by #7537