Travis: test against PHP 7.4

[jrfnl]

Note: for the time being the build will fail.

• PHP-Parallel-Lint itself has an issue - see PHP 7.4: fix deprecation notice #143.
• Looks like the nette/tester package at the ~1.3 version is not compatible with PHP 7.4. The latest release is 2.3.0, but the 2.x branch requires PHP 5.6 for ~2.0 and PHP 7.1 for ^2.1.
  The last release in the 1.x series, 1.7.2 may or may not still contain the issue on which the build is currently failing, but won't be updated anymore either way.
  See: https://github.com/nette/tester/releases
  PR Composer: update nette/tester dependency #147 should fix this.
• PHPCS won't be compatible with PHP 7.4 until version 3.5.0 has been released.
  PR CS: Various phpcs tweaks #146 should fix this part of the build failure.

[jrfnl]

Test build showing that when this + the above mentioned other PRs are all merged, the Travis builds will pass again: https://travis-ci.org/jrfnl/PHP-Parallel-Lint/builds/573466143

[jrfnl]

As PHP 7.4 has come out, I've removed the "allowed to fail" part of the PR and as Travis now has an official PHP 7.4 image available, I've swopped out 7.4snapshot for 7.4.

[grogy]

Hi,

I am using your PR for solve problems. Because author of this great tool does not communicate so I created fork. You can use it from packagist. Now is out new release with PHP 7.4 support.

[jrfnl]

Closing as this has been merged in the new repo: https://github.com/php-parallel-lint/PHP-Parallel-Lint