Fix clippy

[kanru]

No description provided.

[dylanhart]

In response to commit e864117

I appreciate the concern, but I don't think this is the best change for a couple reasons.

1. It requires v0.4.x version bump due to API change (not that big of a deal)
2. It is inconsistent with uuid (see Uuid::new_v4())

I would however approve a change that added a Ulid::nil() method for a zero-valued Ulid. This would allow ulid to implement Default the same way as uuid (see its implementation)

[kanru]

Uuid v4 by spec must be randomly generated. From that point I agree it's nature that Ulid::new() also generate new value every time.

I like the idea of Ulid::nil() as default as it can be used as placeholder value when needed.

[dylanhart]

Thank you! Merging