Test should be for compliance with actual spec

Though the specification may change in the future, the current literature says to throw a SyntaxError here.

Since these tests verify that a user agent complies with the actual literature, and not a proposed future literature, it is appropriate to assert that the thrown assertion is a SyntaxError rather than a TypeError, for the time being.
Merge pull request #974 from caitp/patch-1

Test should be for compliance with actual spec