Upgrade PHPUnit from ^6.5 to ^7.5 and all dependencies, including root differ

[maks-rafalko]

This PR:

• Upgrades PHPUnit from ^6.5 to ^7.5
• Upgrades sebastian/diff to ^3.0 (see composer.lock). This returns back diffs with a context lines (lines before and after a modified one 🎉)
• Run tests in random order by default

Why not PHPUnit 8.0?

It requires PHP ^7.2 while we support 7.1 yet.

Next steps

• integrate pcov
• use --dump-xdebug-filter (see https://thephp.cc/news/2019/01/faster-code-coverage)

---

Had to upgrade dependencies of one of the e2e test because of fatal error:

PHP Fatal error:  Declaration of PHPUnit\Framework\Constraint\ArrayHasKey::matches($other) must be compatible with PHPUnit\Framework\Constraint\Constraint::matches($other): bool in tests/Fixtures/e2e/Save_PHPUnit_Bootstrap_File/vendor/phpunit/phpunit/src/Framework/Constraint/ArrayHasKey.php on line 83

[BackEndTea]

Assuming CI doesn't report anything, 👍

[localheinz]

Looks like --min-msi needs to be adjusted?

See https://travis-ci.org/infection/infection/jobs/492324430#L1117-L1118:

[ERROR] The minimum required MSI percentage should be 90%, but actual is 78%.  
Improve your tests!

[maks-rafalko]

Looks like --min-msi needs to be adjusted?

that's almost impossible in this case, because Infection is run with empty --filter for this PR (https://travis-ci.org/infection/infection/jobs/492324430#L1048)

This is because no PHP source files were modified from src/.

It means that to achieve 90%, I need to do it for the whole project ;) Not feasible indeed.

The goal of this target was to target 90% for the changed files, it just does not work properly with empty filter.

[maks-rafalko]

misread your comment. Ok - the target MSI for changed files is ok to be 90% (original --min-msi=67 in our .travis.yml).

But it shouldn't be 90% when the --filter is empty. This is the issue, but I guess out of the scope of this PR

[maks-rafalko]

Created #631 for MSI issue.

Thank you.