[readable.traits] Use "declare" for typedef-names

Author: frederick-vs-ja

source/iterators.tex

@@ -876,7 +876,7 @@
 
 \pnum
 \begin{note}
-Some legacy output iterators define a nested type named \tcode{value_type}
+Some legacy output iterators declare a nested type named \tcode{value_type}
 that is an alias for \keyword{void}.
 These types are not \libconcept{indirectly_readable}
 and have no associated value types.