[stringstream.members] Add missing param

Author: hewillk

source/iostreams.tex

@@ -9992,7 +9992,7 @@
 \indexlibrarymember{str}{basic_stringstream}%
 \begin{itemdecl}
 template<class T>
-  void str(const T&);
+  void str(const T& t);
 \end{itemdecl}
 
 \begin{itemdescr}