Update version checker

[sergiotejon]

Every run, gommitizen could check if a new version is available and purpose updates it by showing a command.

[sergiotejon]

Use go install for installing instead of using the installation script (https://go.dev/ref/mod#go-install).

This way we can use https://github.com/rhysd/go-github-selfupdate, for example, to autoupdate.