JSON dates should be ISO 8601 format strings

[mikewse]

From mailing list:

When I fetch something which has a Date member then the json contains something like
{
"currentSeason": "N",
"openStatus": "O",
"seasonEndDate": new Date(1543536000000),
"seasonId": 14,
"seasonStartDate": new Date(1512086400000),
},

JSON dates should instead be formated to ISO 8601 strings such as:
2012-04-23T18:25:43.511Z