Fix-up docs for the copyreg module renaming.
diff --git a/Doc/library/persistence.rst b/Doc/library/persistence.rst
index 78e40f6..3708d17 100644
--- a/Doc/library/persistence.rst
+++ b/Doc/library/persistence.rst
@@ -19,7 +19,7 @@
 .. toctree::
 
    pickle.rst
-   copy_reg.rst
+   copyreg.rst
    shelve.rst
    marshal.rst
    anydbm.rst