Renamed property, so it fits with the rest of the nameing

ref #11

src/models/Track.ts

@@ -29,10 +29,10 @@ export class Track {
   name: string;
 
   /**
-   * The track's length in meters.
+   * The track's length/distance in meters.
    */
   @Column()
   @IsInt()
   @IsPositive()
-  length: number;
+  distance: number;
 }