docs: fix typo (#2405)

docs/classes.rst

@@ -74,7 +74,7 @@ Note how ``print(p)`` produced a rather useless summary of our data structure in
     >>> print(p)
     <example.Pet object at 0x10cd98060>
 
-To address this, we could bind an utility function that returns a human-readable
+To address this, we could bind a utility function that returns a human-readable
 summary to the special method slot named ``__repr__``. Unfortunately, there is no
 suitable functionality in the ``Pet`` data structure, and it would be nice if
 we did not have to change it. This can easily be accomplished by binding a