Fix issue #1510

Apparently, the new Character('x') style is deprecated. The fix is
described here:
https://stackoverflow.com/questions/67093884/deprecated-shortstring-how-to-update

bindings/java/org/linkgrammar/JSONReader.java

@@ -39,14 +39,14 @@ public class JSONReader
     private static Map<Character, Character> escapes = new HashMap<Character, Character>();
     static
     {
-        escapes.put(new Character('"'), new Character('"'));
-        escapes.put(new Character('\\'), new Character('\\'));
-        escapes.put(new Character('/'), new Character('/'));
-        escapes.put(new Character('b'), new Character('\b'));
-        escapes.put(new Character('f'), new Character('\f'));
-        escapes.put(new Character('n'), new Character('\n'));
-        escapes.put(new Character('r'), new Character('\r'));
-        escapes.put(new Character('t'), new Character('\t'));
+        escapes.put(Character.valueOf('"'), Character.valueOf('"'));
+        escapes.put(Character.valueOf('\\'), Character.valueOf('\\'));
+        escapes.put(Character.valueOf('/'), Character.valueOf('/'));
+        escapes.put(Character.valueOf('b'), Character.valueOf('\b'));
+        escapes.put(Character.valueOf('f'), Character.valueOf('\f'));
+        escapes.put(Character.valueOf('n'), Character.valueOf('\n'));
+        escapes.put(Character.valueOf('r'), Character.valueOf('\r'));
+        escapes.put(Character.valueOf('t'), Character.valueOf('\t'));
     }
 
     private CharacterIterator it;
@@ -304,7 +304,7 @@ private Object string()
                 }
                 else
                 {
-                    Character value = escapes.get(new Character(c));
+                    Character value = escapes.get(Character.valueOf(c));
                     if (value != null)
                         add(value);
                     else