message: [examples] fix minor clippy warnings
diff: @@ -119,9 +119,9 @@ mod erc20 {
  if from_balance < value {
  return false
  }
  - self.balances.insert(from.clone(), from_balance - value);
  + self.balances.insert(from, from_balance - value);
  let to_balance = self.balance_of_or_zero(&to);
  - self.balances.insert(to.clone(), to_balance + value);
  + self.balances.insert(to, to_balance + value);
  self.env().emit_event(Transfer {
  from: Some(from),
  to: Some(to),
  