message: make "description" field optional in Payout
diff: @@ -143,7 +143,7 @@ pub struct Payout {
  pub balance_transaction: String,
  pub created: Timestamp,
  pub currency: Currency,
  - pub description: String,
  + pub description: Option<String>,
  pub destination: Option<String>,
  pub failure_balance_transaction: Option<String>,
  pub failure_code: Option<PayoutFailureCode>,
  