Invalid StreamHandler Arguments

My application was incorrectly passing the StreamHandler a argument of

```
$stream = array('file://url');
$handler = new StreamHandler($stream);
``` 

And when the stream handler tried to handle a record it would cause the following error
```
Array to string conversion at /var/www/service-manager/vendor/monolog/monolog/src/Monolog/Handler/StreamHandler.php:82
```

I thought by adding an InvalidArgumentException it might show people where they are going wrong quicker
I suggest adding an empty line between the ``@param`` and ``@throws`` tags:

- it will improve readability
- it will make alignment look better (the PHP-CS-Fixer will actually align ``If stream is not a resource or string`` with ``$useLocking``, not with ``Try to lock log file before doing any writes`` as it is in the third segment, while it won't align lines together if they are separated in diffeent blocks)