provide a way to add label for release

beta_releases

add missing option
simplify if/else, use rc php-semver release
Merge pull request #73 from ahilles107/beta_releases

Mark release as beta
Add the composer.lock to git
Following the PR #73, I just add the option to activate (or not) the label management. Most of the users were currently not using the label system, so forced them to always answer 'none' could be painful. To activate it on your project (or a dedicated branch) just add 'allow-label' in your config
Release of new version 1.1.0
notify slack