[range.concat.iterator] Remove superfluous period (#6960)

Author: hewillk

source/ranges.tex

@@ -8726,7 +8726,7 @@
   class concat_view<Views...>::@\exposid{iterator}@ {
 
   public:
-    using iterator_category = @\seebelow@;                                // not always present.
+    using iterator_category = @\seebelow@;                                // not always present
     using iterator_concept = @\seebelow@;
     using value_type = @\exposid{concat-value-t}@<@\exposid{maybe-const}@<Const, Views>...>;
     using difference_type = common_type_t<range_difference_t<@\exposid{maybe-const}@<Const, Views>>...>;