Update the documentation to reflect the changes to ReferenceError.
diff --git a/Doc/lib/libweakref.tex b/Doc/lib/libweakref.tex
index f5887b5..d88b051 100644
--- a/Doc/lib/libweakref.tex
+++ b/Doc/lib/libweakref.tex
@@ -111,7 +111,8 @@
 
 \begin{excdesc}{ReferenceError}
   Exception raised when a proxy object is used but the underlying
-  object has been collected.
+  object has been collected.  This is the same as the standard
+  \exception{ReferenceError} exception.
 \end{excdesc}