[allocator.adaptor.syn] Fix typo in comment in header synopsis

Author: jensmaurer

source/memory.tex

@@ -6311,7 +6311,7 @@
 \indexheader{scoped_allocator}%
 \begin{codeblock}
 namespace std {
-  // class template \tcode{scoped allocator adaptor}
+  // class template \tcode{scoped_allocator_adaptor}
   template<class OuterAlloc, class... InnerAlloc>
     class scoped_allocator_adaptor;