Fix the binary_partition copy constructor. (#1702)

* Fix the `binary_partition` copy constructor.

Prevents issues with older compilers.
\#1683 #1701

* Update src/structure_dump.cpp

Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

src/structure_dump.cpp

@@ -424,7 +424,7 @@ binary_partition::binary_partition(const split_plane &_split_plane,
   if (!left || !right) { meep::abort("Binary partition tree is required to be full"); }
 }
 
-binary_partition::binary_partition(const binary_partition& other) : proc_id{other.proc_id}, plane{other.plane} {
+binary_partition::binary_partition(const binary_partition& other) : proc_id(other.proc_id), plane(other.plane) {
   if (!other.is_leaf()) {
     left.reset(new binary_partition(*other.left));
     right.reset(new binary_partition(*other.right));