JsopBuilder: remove JDK6ism

            default:
                if (c < ' ') {
                    buff.append(String.format("\\u%04x", (int) c));
                } else if (c >= 0xd800 && c <= 0xdbff) {
                    // isSurrogate(), only available in Java 7
                    if (i < length - 1 && Character.isSurrogatePair(c, s.charAt(i + 1))) {
                        // ok surrogate
                        buff.append(c);
                        buff.append(s.charAt(i + 1));
                        i += 1;
                    } else {
                        // broken surrogate -> escape
                        buff.append(String.format("\\u%04x", (int) c));
                    }
                } else {
                    buff.append(c);
                }