Read scmVersion directly from pom

Is impossible to run "mvn scm:bootstrap" without specifing the parameter scmVersionType and scmVersion and retrieve all that I need to checkout a project from the pom because the CheckoutMojo class doesn't read the project/scm/tag value so, by default, checkout the HEAD if no parameter is passing.
This can be trivial if we use this command in a particular configuration in whitch no parameter can be passed to maven and the project is on a different branch

To resolve this issue, I've modified the source code from

@parameter expression="${scmVersion}"

to

@parameter expression="${scmVersion}" default-value="${project.scm.tag}"