Renamed getter

ref #11

src/models/DistanceDonation.ts

@@ -33,7 +33,7 @@ export class DistanceDonation extends Donation {
   public get amount(): number {
     let calculatedAmount = -1;
     try {
-      calculatedAmount = this.amountPerDistance * this.runner.getDistance();
+      calculatedAmount = this.amountPerDistance * this.runner.distance;
     } catch (error) {
       throw error;
     }