[concept.regularinvocable] move iref to a better place

Author: morinmorin

source/concepts.tex

@@ -1107,9 +1107,9 @@
 
 \begin{itemdescr}
 \pnum
-The \tcode{invoke} function call expression shall be equality-preserving and
-shall not modify the function object or the
-arguments\iref{concepts.equality}.
+The \tcode{invoke} function call expression shall be
+equality-preserving\iref{concepts.equality} and
+shall not modify the function object or the arguments.
 \begin{note}
 This requirement supersedes the annotation in the definition of
 \libconcept{invocable}.