Reset static fields visibility to private in YearChecker

Author: Houssem Nasri

jablib/src/main/java/org/jabref/logic/integrity/YearChecker.java

@@ -9,8 +9,8 @@
 
 public class YearChecker implements ValueChecker {
 
-    public static final Predicate<String> CONTAINS_FOUR_DIGIT = Pattern.compile("([^0-9]|^)[0-9]{4}([^0-9]|$)").asPredicate();
-    public static final Predicate<String> ENDS_WITH_FOUR_DIGIT = Pattern.compile("[0-9]{4}$").asPredicate();
+    private static final Predicate<String> CONTAINS_FOUR_DIGIT = Pattern.compile("([^0-9]|^)[0-9]{4}([^0-9]|$)").asPredicate();
+    private static final Predicate<String> ENDS_WITH_FOUR_DIGIT = Pattern.compile("[0-9]{4}$").asPredicate();
     private static final String PUNCTUATION_MARKS = "[(){},.;!?<>%&$]";
 
     /**