Only pass composer json filename to output formatter

[bobvandevijver]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

1. Does your submission pass tests?
2. Have you lint your code locally prior to submission?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Fixes #623. Only the filename of the parsed composer.json is now given to the output parsers. As this file should always be on the root of the project, this should also be correct for the output formatters.

[bobvandevijver]

@icanhazstring Anything I can do to help get this merged and tagged?

[icanhazstring]

Could you come up with a test to verify that?maybe using vfsstream

[bobvandevijver]

I do not know what to test here to be honest, the only real change I added is that the path passed to the formatter no longer is an absolute path, but the filename relative to the project by using a native PHP function.

[bobvandevijver]

@icanhazstring Anything that can be done to get this merged?