[stringbuf.cons] Fix whitespace around reference declarators (#6760)

Author: Andreas-Krug

source/iostreams.tex

@@ -8081,7 +8081,7 @@
 
 \indexlibraryctor{basic_stringbuf}%
 \begin{itemdecl}
-basic_stringbuf(ios_base::openmode which, const Allocator &a);
+basic_stringbuf(ios_base::openmode which, const Allocator& a);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -8119,7 +8119,7 @@
 template<class SAlloc>
   basic_stringbuf(
     const basic_string<charT, traits, SAlloc>& s,
-    ios_base::openmode which, const Allocator &a);
+    ios_base::openmode which, const Allocator& a);
 \end{itemdecl}
 
 \begin{itemdescr}