Update UPGRADE-2.16.md

Co-authored-by: Grégoire Paris <[email protected]>

Author: GromNaN

UPGRADE-2.16.md

@@ -2,7 +2,7 @@
 
 ## Package `doctrine/cache`
 
-The package `doctrine/cache` no longer required.
+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`;