Incrementing minor or major version does not clear lower version components.

[gwadej]

I really like cargo-next as a way to update Cargo.toml version easily.

My one real problem is using the --minor option to update the minor component of the version does not reset the patch version to 0.

So, using cargo next --minor with a version of 0.3.7 gives 0.4.7 instead of the expected 0.4.0.

Of course, I checked the --major flag and found that the same problem exists there.

[gwadej]

Added a PR with a fix: #12