update xtensor includes in test

Author: fbourgin

test/rcpp_tests.cpp

@@ -12,8 +12,8 @@
 
 #include "xtensor-r/rcontainer.hpp"
 #include "xtensor-r/rarray.hpp"
-#include "xtensor/xmath.hpp"
-#include "xtensor/xio.hpp"
+#include "xtensor/core/xmath.hpp"
+#include "xtensor/io/xio.hpp"
 
 // [[Rcpp::export]]
 int modify_cpp(xt::rarray<double>& x)