Fix for windows for cest-classes

this fix is for this issue https://github.com/Codeception/Codeception/issues/254 . I've decided to not modify cest-class name by itself (https://github.com/Codeception/Codeception/blob/master/src/Codeception/TestCase/Cest.php#L124) because in console output it also used and there ```::``` makes sense and easy to read, so i made replacement only in ```PhpBrowser``` when it saves snapshot.
P.S. i will also provide some formatting fix for this file later.