Update UPGRADE.md

Fix minor typo

UPGRADE.md

@@ -13,7 +13,7 @@ instances as mapped by Doctrine.
 ## BC BREAK: Doctrine\DBAL\Schema\Table
 
 The methods ``addIndex()`` and ``addUniqueIndex()`` in ``Doctrine\DBAL\Schema\Table``
-hav an additional, optional parameter. If you override these methods, you should
+have an additional, optional parameter. If you override these methods, you should
 add this new parameter to the declaration of your overridden methods.
 
 ## BC BREAK: Doctrine\DBAL\Connection