feat: allow missing patch

[icorderi]

According to semver 2.0.0, a normal version is defined as:

"A normal version number MUST take the form X.Y.Z where X, Y, and Z are non-negative integers, and MUST NOT contain leading zeroes. X is the major version, Y is the minor version, and Z is the patch version. Each element MUST increase numerically. For instance: 1.9.0 -> 1.10.0 -> 1.11.0."

source: spec-item-2

It is my understanding, and what seems to be common practice in industry that for fresh releases with no patches, a new release version omits the patch value. Essentially, version 1.2 implies 1.2.0, meaning there is no patch yet.

I believe the keyword on the semver spec is the use of normal. A new release is not normal, it's the first version of a new feature with no patch. Therefore an argument can be made that Z can be omitted.

There is an open issue on the matter on semver.

Wikipedia's article on software versioning also omits the 0 on new releases.
wikipedia: software-versioning

[steveklabnik]

For now, I would like to stick to what the spec says here. Which means that I'm not totally opposed, but would like the spec to be clear before I merge. This PR is likely to be valid for a long time though, as it's not like semver is changing much. So thanks! We'll see. 😄

[steveklabnik]

I am going to be sticking with the spec as written for this implementation. Thanks though!