3.0 | Drop support for PHPUnit < 6.4

[jrfnl]

Drop support for PHPUnit < 6.4 [1]

Adjust CI, README and composer.json for the drop of support for PHPUnit < 6.4.4.

The 6.4.4 version is a deliberate choice to allow for dropping:

• The ExpectExceptionObject polyfill (native method was introduced in PHPUnit 6.4.0 with bugfix in PHPUnit 6.4.4)
• A work-around in the AssertStringContains polyfills for a bug which was fixed in PHPUnit 6.4.2.
• And not requiring a call to expectException() for a call to expectExceptionMessage() (bug fixed in PHPUnit 6.4.3).

Drop support for PHPUnit < 6.4 [2]

Remove the ExpectExceptionObject polyfill and all references to it.

Drop support for PHPUnit < 6.4 [3]

As the minimum supported PHPUnit version will be PHPUnit 6.4.4, the AssertStringContains logic can be reverted to the original logic and no longer needs to account for the PHPUnit < 6.4.2 bug with mb_strpos().

Drop support for PHPUnit < 6.4 [4]

Even though the TestListener implementation is not (yet) compatible with PHPUnit 10 (nor 11), we should still drop support for PHPUnit < 6.4 from the existing implementation.

Drop support for PHPUnit < 6.4 [5]

Remove work-arounds for PHPUnit 5.x from the test suite.

[coveralls]

coverage: 97.143% (+0.7%) from 96.423% when pulling 1ea653a3bc73b7d0ce00d4d39aa3d0b9d98e3eef on feature/3.x/drop-support-for-phpunit-lt-64 into 805f0bae96d921d7fa9b29d799341105986fc76f on 3.x.