added trial_from_plan to ISubscriptionCustCreationOptions interface (#27820)

This property was added to the Stripe API on 2018-05-21

[API Change Log](https://stripe.com/docs/upgrades#2018-05-21)
[API Docs](https://stripe.com/docs/api#create_subscription-trial_from_plan)

types/stripe/index.d.ts

@@ -4679,6 +4679,12 @@ declare namespace Stripe {
              */
             trial_period_days?: number;
 
+            /**
+             * Indicates if a plan’s trial_period_days should be applied to the subscription. Setting trial_end per subscription is preferred, 
+             * and this defaults to false. Setting this flag to true together with trial_end is not allowed.
+             */
+            trial_from_plan?: boolean;
+
             /**
              * List of subscription items, each with an attached plan.
              */