Update to 0.17.1 breaks approx-feature

[bgschaid]

When changing from
ndarray = { version = "0.16.1", features = ["approx"] }
to
ndarray = { version = "0.17.1", features = ["approx"] }
unit-tests that previously worked don't compile with

error[E0599]: no method named `abs_diff_eq` found for struct `ArrayBase<S, D>` in the current scope
   --> src/tracedown/types.rs:166:26
    |
166 |         assert!(original.abs_diff_eq(&result, tol));
    |                          ^^^^^^^^^^^ method not found in `ArrayBase<OwnedRepr<f32>, Dim<[usize; 2]>>`