Use "new" method for fraction

src/bin/problem_26.rs

@@ -9,10 +9,7 @@ fn main() {
     println!("Start");
     let mut longest = (0, 0);
     for denominator in 2..1000 {
-        let f = Fraction {
-            numerator: 1.into(),
-            denominator: denominator.into(),
-        };
+        let f = Fraction::new(1.into(), denominator.into()).unwrap();
         if let Some(rep) = get_recurring(&f) {
             if longest.1 < rep.digits.len() {
                 longest = (denominator, rep.digits.len());