Update XSD schema version for MATSim's vehicles.xml file

[KasiaKoz]

Currently, we output vehicles to MATSim xml file using v1 DTD schema.

We should update genet to use the more recent v2 DTD schema - this is the version that MATSim will output, post simulation.
Its includes new data fields that are currently being defaulted, the most worrying one being networkMode="car". I don't think it makes any difference in simulation currently, but we should update in case this changes in the future.