confusingly need std:: namespace on for_each

Former-commit-id: 39481eda3fb2a32b4f698260db4fecff41f4ee4c

include/igl/directed_edge_parents.cpp

@@ -24,7 +24,7 @@ IGL_INLINE void igl::directed_edge_parents(
   slice_into(colon<int>(0,E.rows()-1),E.col(1).eval(),I);
   VectorXi roots,_;
   setdiff(E.col(0).eval(),E.col(1).eval(),roots,_);
-  for_each(roots.data(),roots.data()+roots.size(),[&](int r){I(r)=-1;});
+  std::for_each(roots.data(),roots.data()+roots.size(),[&](int r){I(r)=-1;});
   slice(I,E.col(0).eval(),P);
 }