fix: renamed train files

src/main/java/oving7/train/TrainCar.java

@@ -3,7 +3,7 @@ package oving7.train;
 /**
  * The class {@code TrainCar} represents a simple and general train car.
  */
-public class TrainCarDocs {
+public class TrainCar {
 
     // TODO: Add fields here
 
@@ -15,7 +15,7 @@ public class TrainCarDocs {
      * 
      * @see TrainCarTest#testDeadWeight()
      */
-    public TrainCarDocs(int deadWeight) {
+    public TrainCar(int deadWeight) {
         // TODO: Implement this constructor
     }