fix typo "following" (#91)

examples/single_logger.php

@@ -7,5 +7,5 @@
 $logger->pushHandler(new Monolog\Handler\StreamHandler('php://stdout'));
 $logger->info('Hellooooo World!');
 
-// you should see the follwing in the stdout:
+// you should see the following in the stdout:
 //    [YYYY-mm-dd hh:mm:ss] some_logger.INFO: Hellooooo World!