Fixed typo in the Tree widget bindings' docs

Author: pthebaul

src/textual/widgets/_tree.py

@@ -553,7 +553,7 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
     | Key(s) | Description |
     | :- | :- |
     | enter | Select the current item. |
-    | space | Toggle the expand/collapsed space of the current item. |
+    | space | Toggle the expand/collapsed state of the current item. |
     | up | Move the cursor up. |
     | down | Move the cursor down. |
     """