Fix rcond_hilbert test

[gkobeaga]

The test rcond_hilbert was failing with a Lapack return_code: -5, since some elements of the matrix were Inf (when i+j-1=0).

Test error:

---- rcond_hilbert stdout ----
thread 'rcond_hilbert' panicked at ndarray-linalg/tests/solve.rs:263:5:
called `Result::unwrap()` on an `Err` value: Lapack(LapackInvalidValue { return_code: -5 })

[bluss]

lgtm

[bluss]

Thanks!