public String toString() {
            StringBuilder buffer = new StringBuilder();
            for (Item item : this) {
                if (buffer.length() > 0) {
                    buffer.append((item instanceof ListItem) ? '-' : '.');
                }
                buffer.append(item);
            }
            return buffer.toString();
        }
Represents a version list item. This class is used both for the global item list and for sub-lists (which start
with '-(number)' in the version specification).
plugin/src/main/java/com/mcxiaoke/packer/ng/StringVersion.java