Typo (#652)

environnement = environment

Author: PhilETaylor

docs/topics/memory_saving.md

@@ -43,7 +43,7 @@ usage of PhpSpreadsheet.
 ## Common use cases
 
 PhpSpreadsheet does not ship with alternative cache implementation. It is up to
-you to select the most appropriate implementation for your environnement. You
+you to select the most appropriate implementation for your environment. You
 can either implement [PSR-16](http://www.php-fig.org/psr/psr-16/) from scratch,
 or use [pre-existing libraries](https://packagist.org/search/?q=psr-16).