[www] Fix build of attribute documentation.

clang/include/clang/Basic/AttrDocs.td

@@ -3035,7 +3035,7 @@ supported in C++.
 By default, a reference is considered to refer to its referenced object, a
 pointer is considered to refer to its pointee, a ``std::initializer_list<T>``
 is considered to refer to its underlying array, and aggregates (arrays and
-simple ``struct``s) are considered to refer to all objects that their
+simple ``struct``\s) are considered to refer to all objects that their
 transitive subobjects refer to.
 
 Clang warns if it is able to detect that an object or reference refers to