small typo corrected

src/mpi14/RecvDynamicSize.hpp

@@ -32,7 +32,7 @@ namespace mpi14 {
   public:
 
     /// Constructor with user receive-functor `R`.
-    template <class F,
+    template <class R,
       REQUIRES( concepts::Callable<R(MPI_Status)> )>
     RecvDynamicSize(int from, int tag, MPI_Comm comm, R&& r)
       : from_(from)