message: Add customer param to charge param
diff: @@ -90,6 +90,8 @@ pub struct ChargeParams<'a> {
  #[serde(skip_serializing_if = "Option::is_none")]
  pub shipping: Option<ShippingDetails>,
  #[serde(skip_serializing_if = "Option::is_none")]
  + pub customer: Option<String>,
  + #[serde(skip_serializing_if = "Option::is_none")]
  pub source: Option<CustomerSource<'a>>,
  #[serde(skip_serializing_if = "Option::is_none")]
  pub statement_descriptor: Option<&'a str>,
  