Always follow link header if content-type is not json.

[JulienPalard]

Trying myself at #129 (comment)

Fixes #128
Ref #129

Highly inspired from #129, but trying myself at it.

Master before and after this PR has the same set of failing tests:

FAILED (failures=5, errors=2, skipped=30)
OK (skipped=1)
OK (skipped=3)

The tests provided in #129 are passing, and:

print(
    json.dumps(
        jsonld.expand(
            {
                "@context": "http://schema.org/",
                "@type": "Person",
                "name": "Jane Doe",
                "jobTitle": "Professor",
                "telephone": "(425) 123-4567",
                "url": "http://www.janedoe.com",
            }
        ),
        indent=4,
    )
)

now passes too.

[JulienPalard]

I'd like to add some tests to the test suite, but I don't understand how to do so. If someone can explain before merging I'd gladly do so.