title: Add Discount to Braintree Rails Transaction
body: <p>Is there any way to add discounts to braintree transaction. I know it is possible to do so on subscriptions, but i want to add it to a non recurring billing transaction. Here is what i have tried which works fine with <code>Braintree::Subcription.create</code></p>
  <pre><code>result = gateway.transaction.sale(
        amount: amount,
        payment_method_token: token_generated,
        options: {
          submit_for_settlement: true
        },
        discounts: {
          add: [
              {
                inherited_from_id: &quot;2rhw&quot;
              }
            ]
          }
      )
  </code></pre>
  <p>This gives me the invalid key error for discounts and add. Is there a walkaround for this or adding a discount to single transaction is not possible.</p>