Fix typo nesetedset

Author: juukie

UPGRADE.markdown

@@ -1,7 +1,7 @@
 ### Upgrading from 4.0 to 4.1
 
-Nested sets feature has been moved to trait `Kalnoy\Nesetedset\NodeTrait`, but
-old `Kalnoy\Nesetedset\Node` class is still available.
+Nested sets feature has been moved to trait `Kalnoy\Nestedset\NodeTrait`, but
+old `Kalnoy\Nestedset\Node` class is still available.
 
 Some methods on trait were renamed (see changelog), but still available on legacy
 node class.
@@ -25,4 +25,4 @@ you should call `defaultOrder` on the query.
 
 Since root node is not required now, `NestedSet::createRoot` method has been removed.
 
-`NestedSet::columns` now doesn't create a foreign key for a `parent_id` column.
+`NestedSet::columns` now doesn't create a foreign key for a `parent_id` column.