Add requirements for JSON validation of dates and URIs
Add requirements for JSON validation of dates and URIs

The json formatter wasn't validating dates and URIs because these packages have been missing until now.
See here for details: https://python-jsonschema.readthedocs.org/en/latest/validate/#validating-formats

alphagov/digitalmarketplace-api,alphagov/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,mtekel/digitalmarketplace-api,mtekel/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,mtekel/digitalmarketplace-api,mtekel/digitalmarketplace-api,RichardKnop/digitalmarketplace-api,alphagov/digitalmarketplace-api,RichardKnop/digitalmarketplace-api