message: Add delete subscription params
diff: @@ -2,6 +2,7 @@ use error::Error;
  use client::Client;
  use resources::{Discount, Plan};
  use params::{List, Metadata, Timestamp};
  +use serde_qs as query;
  #[derive(Default, Serialize)]
  pub struct CancelParams {
  @@ -97,6 +98,6 @@ impl Subscription {
  ///
  /// For more details see https://stripe.com/docs/api#cancel_subscription.
  pub fn cancel(client: &Client, subscription_id: &str, params: CancelParams) -> Result<Subscription, Error> {
  - client.post(&format!("/subscriptions/{}/cancel", subscription_id), params)
  + client.delete(&format!("/subscriptions/{}?{}", subscription_id, query::to_string(&params)?))
  }
  }
  