assert_relative_eq! does not compile for DMatrix and Matrix2xX

I use the latest `approx` 0.5.1 with `nalgebra` 0.31.4 (both latest).
Consider the following code:
```rust
let a: Matrix, Dynamic, VecStorage, Dynamic>> = result();
let b: Matrix> = expected();
a.relative_eq(&b, 0.1, 0.1); // Compiles
assert_relative_eq!(result_table, expected_result_table); // Error
```
Compile error:
```
mismatched types
expected reference `&Matrix, Dynamic, VecStorage, Dynamic>>`
found reference `&Matrix>`
```