Solve conflic with num-traits (#130)

* Solve conflic with num-traits

* Fix clippy warnings

Co-authored-by: Luis Moreno <morenol@users.noreply.github.com>

src/linear/logistic_regression.rs

@@ -321,7 +321,7 @@ impl<T: RealNumber, M: Matrix<T>> LogisticRegression<T, M> {
 
         if x_nrows != y_nrows {
             return Err(Failed::fit(
-                &"Number of rows of X doesn\'t match number of rows of Y".to_string(),
+                "Number of rows of X doesn\'t match number of rows of Y",
             ));
         }