[iterator.concept.forward] Undo spurious list item capitalization. (#4017)

Author: Eelis

source/iterators.tex

@@ -1706,7 +1706,7 @@
 offer the \defn{multi-pass guarantee} if:
 \begin{itemize}
 \item \tcode{a == b} implies \tcode{++a == ++b} and
-\item The expression
+\item the expression
 \tcode{((void)[](X x)\{++x;\}(a), *a)} is equivalent to the expression \tcode{*a}.
 \end{itemize}