reduce visibility for getHighestInteger(), only needed for tests

pdb-api/src/main/java/org/lucares/pdb/api/UniqueStringIntegerPairs.java

@@ -188,7 +188,7 @@ public class UniqueStringIntegerPairs {
         return intToString.get(second);
     }
 
-    public Integer getHighestInteger() {
+    Integer getHighestInteger() {
         return intToString.size() == 0 ? -1 : intToString.size() - 1;
     }