fix overflow issue in 32bit doctest

Author: orxfun

src/tree.rs

@@ -1052,7 +1052,7 @@ where
     /// use orx_tree::*;
     ///
     /// let num_children = 4;
-    /// let total_depth = 10;
+    /// let total_depth = 6;
     ///
     /// let mut tree = DynTree::new(0.to_string());
     /// let mut dfs = Traversal.dfs().over_nodes();