Remove ParallelStream.filter for trivial operation

lib/dynamic_programming_in_elixir.ex

@@ -56,7 +56,7 @@ defmodule DynamicProgrammingInElixir do
       else
         in_edges
         |> ParallelStream.map(fn edge -> calculate_current_path(g, source, edge) end)
-        |> ParallelStream.filter(fn x -> elem(x, 0) == :ok end)
+        |> Enum.filter(fn x -> elem(x, 0) == :ok end)
         |> Enum.to_list()
         |> my_min()
       end