Fix mistake in UPGRADING

UPGRADING

@@ -29,7 +29,7 @@ PHP 7.2 UPGRADE NOTES
     integer keys to string property names. This fixes the behaviour of previous
     versions, where integer keys would become inaccessible properties with
     integer names.
-  . Casting objects to arrays (with (object) or settype()), and retrieving
+  . Casting objects to arrays (with (array) or settype()), and retrieving
     object properties in an array with get_object_vars(), will now convert
     numeric string property names (that is, property names of the format
     /^(0|(-?[1-9][0-9]*))$/ where PHP_INT_MIN <= n <= PHP_INT_MAX) to integer