Add missing impls to *InverseGaussian errors

rand_distr/src/inverse_gaussian.rs

@@ -3,7 +3,7 @@ use num_traits::Float;
 use rand::Rng;
 
 /// Error type returned from `InverseGaussian::new`
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Error {
     /// `mean <= 0` or `nan`.
     MeanNegativeOrNull,

rand_distr/src/normal_inverse_gaussian.rs

@@ -3,7 +3,7 @@ use num_traits::Float;
 use rand::Rng;
 
 /// Error type returned from `NormalInverseGaussian::new`
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Error {
     /// `alpha <= 0` or `nan`.
     AlphaNegativeOrNull,