Set default mimeType for NtriplesRDFDatastream to 'application/n-triples'
per W3C recommendation.
http://www.w3.org/TR/n-triples/#n-triples-mediatype
Fixes #464
Merge pull request #465 from dchandekstark/n-triples-mime-type

Set default mimeType for NtriplesRDFDatastream to 'application/n-triples'
RdfDatastream#deserialize should always return an RDF::Graph. Fixes #471
Merge pull request #472 from projecthydra/deserialize_returns_graph

RdfDatastream#deserialize should always return an RDF::Graph. Fixes #471
Bump version to 7.1.1