Remove code smells by Changing constructor's visibility in the abstract classes "Card" & "Mission"

risk-server/src/main/java/org/nominoe/datatypes/card/Card.java

@@ -13,7 +13,7 @@ public abstract class Card implements Entity {
 
     private SingleReference<Player> player;
 
-    public Card() {
+    protected Card() {
         this.player = new SingleReferencePlayerToCard(this);
     }
 

risk-server/src/main/java/org/nominoe/datatypes/mission/Mission.java

@@ -26,7 +26,7 @@ public abstract class Mission implements Entity {
      *Constructor with parameters.
      *@param objective the objective of the mission.
      */
-    public Mission(String objective) {
+    protected Mission(String objective) {
         this.objective = objective;
     }