The JoinType properties of a relationship in MDL should be case insensitive

[goldmedal]

Description

I found the join type should now be set in lowercase.

    {
      "name": "orders_customer",
      "models": [
        "orders",
        "customers"
      ],
      "joinType": "many_to_one",
      "condition": "orders.customer_id = customers.id",
      "properties": []
    },

However, it should actually be case insensitive.