Update README.md - fix link for visitors

Author: andyw8

README.md

@@ -525,7 +525,7 @@ With visitors, you only define handlers for the nodes that you need. You can fin
 * call `visit(child)` with each child that you want to visit
 * call nothing if you're sure you don't want to descend further
 
-There are a couple of visitors that ship with Syntax Tree that can be used as examples. They live in the [lib/syntax_tree/visitor](lib/syntax_tree/visitor) directory.
+There are a couple of visitors that ship with Syntax Tree that can be used as examples. They live in the [lib/syntax_tree](lib/syntax_tree) directory.
 
 ### visit_method