Bug in learn_paths_rpi

There is a small bug in learn_paths_rpi, which leads to incorrect output of gpi. If [this line](https://github.com/MegamindHenry/JudiLing.jl/blob/daf3e210d9bd8c5042ea53298bee63bd3b4b2c93/src/find_path.jl#L870) and the following one would be exchanged, it should be correct.