Add warning about wrong regex form in Assert::match() in tester output

[petrparolek]

Example:

$pattern = "sign/in";
$actual = "https://test.dev/sign/in?_fid=j3o0";
\Tester\Assert::match($pattern, $actual);

Current tester output:

Failed: 'https://test.dev/sign/in?_fid=j3o0' should match
       ... 'sign/in' in testAbc()

It would nice something like:

Failed: 'wrong pattern format given.'
Failed: 'https://test.dev/sign/in?_fid=j3o0' should match
       ... 'sign/in' in testAbc()

[milo]

Related to #350