[Backport] Changed property position at directory country source class

[arnoudhgz]

Original Pull Request

#17444
A property wasn't in the best place

Description

Property $_options wasn't in the best place at \Magento\Directory\Model\Config\Source\Country class so I moved it where it should be

Fixed Issues (if relevant)

Code style improvement

Manual testing scenarios

N/A

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[sidolov]

Hi @arnoudhgz , due to changes in Magento Code Contributions Guide we can't accept such Pull Requests to 2.1 release line. All code cleanup like typos, spelling mistakes, removing unused code, etc should be delivered to 2.3 release line.
Thank you!