[move.iter.cons] Add missing Returns

Author: hewillk

source/iterators.tex

@@ -4279,6 +4279,10 @@
 \effects
 Assigns \tcode{u.current} to
 \tcode{current}.
+
+\pnum
+\returns
+\tcode{*this}.
 \end{itemdescr}
 
 \rSec3[move.iter.op.conv]{Conversion}