Fixed quantize syntax.

Doc/lib/libdecimal.tex

@@ -378,7 +378,7 @@ also have a number of specialized methods:
 \end{methoddesc}                                              
 
 \begin{methoddesc}{quantize}
-  {\optional{exp \optional{, rounding\optional{, context\optional{, watchexp}}}}}
+  {exp \optional{, rounding\optional{, context\optional{, watchexp}}}}
   Quantize makes the exponent the same as \var{exp}.  Searches for a
   rounding method in \var{rounding}, then in \var{context}, and then
   in the current context.