[time.clock.utc.nonmembers] fix \end{itemdescr}

Author: timsong-cpp

source/time.tex

@@ -2815,6 +2815,7 @@
 \tcode{elapsed} is the number of leap seconds between 1970-01-01 and \tcode{ut}.
 If \tcode{is_leap_second} is \tcode{true},
 the leap second referred to by \tcode{ut} is included in the count.
+\end{itemdescr}
 
 \rSec2[time.clock.tai]{Class \tcode{tai_clock}}
 
@@ -2861,7 +2862,6 @@
 \begin{note}
 \tcode{noexcept(from_utc(utc_clock::now()))} is \tcode{false}.
 \end{note}
-\end{itemdescr}
 
 \rSec3[time.clock.tai.members]{Member functions}