Update GitlabRepository.getProjectForPath() to no longer require an admin user

In our usage of this plug-in, we'd like to restrict the bot user to the most restricted access possible.

Please note that this change is based on @bjaglin's #59 as I was unable to save the job config without his fix.

* Updated GitlabRepository.getProjectForPath() to use the non-admin /projects endpoint via GitlabAPI.getProjects(). This allows the use of a user with just the [Reporter](http://doc.gitlab.com/ce/permissions/permissions.html) role.
* Updated the Jenkins version in pom.xml.