Correcting a typo

;)

README.md

@@ -332,7 +332,7 @@ You can ask some questions to your Baum nodes:
 * `isAncestorOf($other)`: Returns true if node is an ancestor of the other.
 * `isSelfOrAncestorOf($other)`: Returns true if node is self or an ancestor.
 * `equals($node)`: current node instance equals the other.
-* `insideSubtree($node)`: Checks wether the given node is inside the subtree
+* `insideSubtree($node)`: Checks whether the given node is inside the subtree
 defined by the left and right indices.
 * `inSameScope($node)`: Returns true if the given node is in the same scope
 as the current one. That is, if *every* column in the `scoped` property has