add type declaration in test

Author: Mec-iS

src/linear/logistic_regression.rs

@@ -829,7 +829,7 @@ mod tests {
     #[test]
     #[cfg(feature = "serde")]
     fn serde() {
-        let x = DenseMatrix::from_2d_array(&[
+        let x: DenseMatrix<f32> = DenseMatrix::from_2d_array(&[
             &[1., -5.],
             &[2., 5.],
             &[3., -2.],