[concept.equivalencerelation] Rename to [concept.equiv].

Author: zygoloid

source/concepts.tex

@@ -256,7 +256,7 @@
   template<class R, class T, class U>
     concept relation = @\seebelow@;
 
-  // \ref{concept.equivalencerelation}, concept \libconcept{equivalence_relation}
+  // \ref{concept.equiv}, concept \libconcept{equivalence_relation}
   template<class R, class T, class U>
     concept equivalence_relation = @\seebelow@;
 
@@ -1125,7 +1125,7 @@
     predicate<R, T, U> && predicate<R, U, T>;
 \end{itemdecl}
 
-\rSec2[concept.equivalencerelation]{Concept \cname{equivalence_relation}}
+\rSec2[concept.equiv]{Concept \cname{equivalence_relation}}
 
 \begin{itemdecl}
 template<class R, class T, class U>