Fix fromRdf-0020-out.jsonld by ordering nodes properly

Step 7 in the Serialize RDF as JSON-LD Algorithm sorts the nodes in ascending order ('_' precedes 'h').
Add new corner-case test for #357

The algorithm update in 3f31c3cc750632f76e8c644fad6f5c95e642fa2f doesn't fully address the issue.

/cc @gkellogg @dlongley