Update the include headers pointing to v3 of behaviortree_cpp library

[ashishraste]

Hi Davide,

Thanks for setting up this example ROS repo.

I've updated the headers pointing to behaviortree_cpp_v3 instead of (possibly older?) behaviortree_cpp library. I believe this is required since the package being referred to is behaviortree_cpp_v3.

cheers, Ashish

[Timple]

This change seems to be already in.

[renan028]

thanks, but I am closing since we are moving to bt.v4