Update docs/resources/Subscription.md

Co-authored-by: Mihail Gribkov <[email protected]>

Author: colinloretz

docs/resources/Subscription.md

@@ -18,7 +18,7 @@ Subscriptions in Discord represent a user making recurring payments for at least
 | current_period_start | ISO8601 timestamp    | Start of the current subscription period                                                                                                   |
 | current_period_end   | ISO8601 timestamp    | End of the current subscription period                                                                                                     |
 | status               | SubscriptionStatus   | Current status of the subscription                                                                                                         |
-| canceled_at          | ISO8601 timestamp?   | When the subscription was canceled                                                                                                         |
+| canceled_at          | ?ISO8601 timestamp   | When the subscription was canceled                                                                                                         |
 | country?             | string               | ISO3166-1 alpha-2 country code of the payment source used to purchase the subscription. Missing unless queried with a private OAuth scope. |
 
 The start of a subscription is determined by its ID. When the subscription renews, its current period is updated.