Enable json5 and json-stringify parsers by default (#92)

[aspiers]

These two parsers were accidentally omitted from the default list. In particular, this broke the choice of parser for package.json files. So add them to the default list.

This solves the original motivating factor for #92, but not #92 itself which is a request for enhanced debugging capabilities.

[jscheid]

Thanks @aspiers. See if you can figure out the failing test, otherwise I'll try and have a look soon.

[aspiers]

I can't immediately, and weirdly I get a different failure when running the tests locally!

[jscheid]

See #96