allergies: update reference and starter implementations

exercises/allergies/.meta/src/reference/java/Allergen.java

-public enum Allergen {
+enum Allergen {
     EGGS(1),
     PEANUTS(2),
     SHELLFISH(4),
         this.score = score;
     }
 
-    public int getScore() {
+    int getScore() {
         return score;
     }
 }

exercises/allergies/.meta/src/reference/java/Allergies.java

 import java.util.List;
 import java.util.stream.Collectors;
 
-public class Allergies {
+class Allergies {
 
     private int score;
 
-    public Allergies(int score) {
+    Allergies(int score) {
         this.score = score;
     }
 
-    public List<Allergen> getList() {
+    List<Allergen> getList() {
         return EnumSet.allOf(Allergen.class).stream()
                 .filter(this::isAllergicTo)
                 .collect(Collectors.toList());
     }
 
-    public boolean isAllergicTo(Allergen allergen) {
+    boolean isAllergicTo(Allergen allergen) {
         return (score & allergen.getScore()) == allergen.getScore();
     }
 }

exercises/allergies/src/main/java/Allergen.java

-public enum Allergen {
+enum Allergen {
     EGGS(1),
     PEANUTS(2),
     SHELLFISH(4),
         this.score = score;
     }
 
-    public int getScore() {
+    int getScore() {
         return score;
     }
 }