Relax trait bounds for Default implementation

[jonasbb]

The Default derive adds a T: Default and a N: Default bound on the implementation. The T: Default bound is however not necessary and can be removed by manually implementing Default.

It might also be worth to consider changing the bounds to N: Zero, to bring it in line with most other trait implementations. This would, however, change Default in non-backwards compatible ways, which is why I didn't attempt that.

[coriolinus]

Thanks for spotting / improving this! Agree that we shouldn't add N: Zero in this case. Will push a point release shortly.