Tidy up amount calculation

src/transaction.rs

@@ -18,9 +18,7 @@ fn parse_amount_str(amount_str: &str) -> Result<i64, Error> {
     let frac = format!("{:0<2}", frac);
     let frac = frac.parse::<i64>()?;
 
-    let mut amount: i64 = 0;
-    amount += whole * 100 * 10;
-    amount += frac * 10;
+    let amount = whole * 100 * 10 + frac * 10;
     Ok(if negative { -amount } else { amount })
 }