Migrating to assertStringContainsString PHPUnit 8.x

[peter279k]

As title, after upgrading PHPUnit version, it will have following warning message:

[PHPUnit\Framework\Warning] Using assertContains() with string haystacks is deprecated and will not be supported in PHPUnit 9. Refactor your test to use assertStringContainsString() or assertStringContainsStringIgnoringCase() instead.

And it should change into assertStringContainsString and assertStringNotContainsString assertions.

[gordalina]

Added in version 5.0.0. Check the changelog