Make dates in VCR mock files relative.
Make dates in VCR mock files relative.

leftees/trade-tariff-backend,alphagov/trade-tariff-backend,bitzesty/trade-tariff-backend,bitzesty/trade-tariff-backend,alphagov/trade-tariff-backend,bitzesty/trade-tariff-backend,leftees/trade-tariff-backend,leftees/trade-tariff-backend,alphagov/trade-tariff-backend