Updating the wanted error for testdata/UnexportedStruct

[loudej]

adding "name" because runtests.sh reports:

        wire_test.go:121: Errors didn't match expected errors from wire_errors.txt:
            {[]string}[0]:
                -: "example.com/foo/wire.go:x:y: name foo not exported by package bar"
                +: "example.com/foo/wire.go:x:y: foo not exported by package bar"

Fixes #412