Bump org.apache.maven.scm dependencies to be able to support Git v1.9.1.

Related to issue: https://issues.jenkins-ci.org/browse/JENKINS-22820
Update Plexus components so Git-related tests will pass.
Merge pull request #21 from rogerhu/jenkins_22820

[JENKINS-22820] fix - Bump maven.scm to 1.9.1 to avoid issues with Git v1.9 upgrades.