Test enhancment for PHPUnit fixtures and version

[peter279k]

Changed log

• It seems that the package requires php-7.1 version at least. Setting the correct version semver for PHP.
• Removing some invalid attributes on phpunit.xml.dist file.

These invalid attribute messages are as follows:

Line 10:
  - Element 'phpunit', attribute 'mapTestClassNameToCoveredClassName': The attribute 'mapTestClassNameToCoveredClassName' is not allowed.
  - Element 'phpunit', attribute 'strict': The attribute 'strict' is not allowed.

  Line 21:
  - Element 'log', attribute 'title': The attribute 'title' is not allowed.
  - Element 'log', attribute 'charset': The attribute 'charset' is not allowed.
  - Element 'log', attribute 'yui': The attribute 'yui' is not allowed.
  - Element 'log', attribute 'highlight': The attribute 'highlight' is not allowed.

  Line 23:
  - Element 'log', attribute 'logIncompleteSkipped': The attribute 'logIncompleteSkipped' is not allowed.

  Line 27:
  - Element 'blacklist': This element is not expected. Expected is ( whitelist ).

• According to the official PHPUnit doc, it should be protected function setUp(): void and protected function tearDown(): void.