switch to new location of goyaml

The old one doesn't even build anymore.

    ~/src/launchpad.net/goyaml $ go install
    # launchpad.net/goyaml
    ./decode.go:34:17: error: type name requires a specifier or qualifier
    ./decode.go:34:17: error: expected member name or ';' after declaration specifiers
    ./decode.go:34:17: error: expected ';' at end of declaration list