Fix the yaml parser bug when running in windows

I have used **php-vcr** in my project. When unit testing, the PHPUnit failed silently if I using Yaml storage. The problem is solved when I change the storage method from Yaml into Json.
 
After looking into the **php-vcr** source code. I believe that the bug comes from  [this line of code](https://github.com/php-vcr/php-vcr/blob/master/src/VCR/Storage/Yaml.php#L132). In windows, the `PHP_EOL` consists of two character, which make the condition `$lastChar === PHP_EOL` never true.