updated if let to latest swift

Author: AakifFRT

source-cn/behavioral/chain_of_responsibility.swift

@@ -47,7 +47,7 @@ final class MoneyPile: Withdrawing {
  return true
  }
 
- if let next = self.next {
+ if let next {
  return next.withdraw(amount: amount)
  }
 

source/behavioral/chain_of_responsibility.swift

@@ -47,7 +47,7 @@ final class MoneyPile: Withdrawing {
  return true
  }
 
- if let next = self.next {
+ if let next {
  return next.withdraw(amount: amount)
  }