Update UPGRADE-2.16.md

Co-authored-by: Jeremy Mikola <jmikola@gmail.com>

Author: GromNaN

UPGRADE-2.16.md

@@ -5,6 +5,6 @@
 The package `doctrine/cache` is no longer required.
 
 If you use `Doctrine\ODM\MongoDB\Configuration::getMetadataCacheImpl()`,
-then you need to require `doctrine/cache` explicitly in your `composer.json`;
+then you need to require `doctrine/cache` explicitly in `composer.json`;
 or use `Doctrine\ODM\MongoDB\Configuration::getMetadataCache()` instead.