Fix stats parsing for haproxy 2.3

[vooon]

Pull Request Checklist

Fixes #50.

General

• [x] Update Changelog following the conventions laid out on Our CHANGELOG Guidelines

• [ ] Update README with any necessary configuration snippets

• [ ] Binstubs are created if needed

• [ ] RuboCop passes

• [x] Existing tests pass

New Plugins

• [ ] Tests

• [ ] Add the plugin to the README

• [ ] Does it have a complete header as outlined here

Purpose

Known Compatibility Issues

[majormoses]

closing in favor of #54 and is released as https://rubygems.org/gems/sensu-plugins-haproxy/versions/2.0.3