Incrementing major version should reset minor and patch version

[tramfjord]

According to https://semver.org/#spec-item-8:

Patch and minor versions MUST be reset to 0 when major version is incremented.

the README basically demonstrates this bug in this project.

[leehericks]

The current code does this correctly, please see the increment! method.

Depending on which part is incremented, :major, :minor or :patch, the lower parts will be zeroed and :pre and :build will be set to nil.