message: added dyn to callback
diff: @@ -17,7 +17,7 @@ use std;
  use std::default::Default;
  use std::f64;
  -type Callback<T> = FnMut(&T, f64, &Vec<Particle<T>>) -> ();
  +type Callback<T> = dyn FnMut(&T, f64, &Vec<Particle<T>>) -> ();
  /// Particle Swarm Optimization (PSO)
  ///
  