[range.elements.iterator] Add missing \expos comment (#3609)

Author: JohelEGP

source/ranges.tex

@@ -6188,7 +6188,7 @@
   template<class V, size_t N>
   template<bool Const>
   class elements_view<V, N>::@\exposid{iterator}@ {                 // \expos
-    using @\exposid{base-t}@ = conditional_t<Const, const V, V>;
+    using @\exposid{base-t}@ = conditional_t<Const, const V, V>;    // \expos
     friend @\exposid{iterator}@<!Const>;
 
     iterator_t<@\exposid{base-t}@> @\exposid{current_}@;