getVersion() use wrong class for calculating PF4J version

[janhoy]

I have a custom PluginManager, and when the getVersion() code attempts to log PF4J's version in initialize(), it uses getClass() to fetch implementationVersion. This assumes that getClass returns a PF4J class, but it returns my own class, which incidentially has a version not parsable by semVer Version class (it contains a space and git hash after the version string).

The fix is to always use a pf4j class for calculating the version.

[coveralls]

Coverage increased (+0.03%) to 23.718% when pulling 69601ec on cominvent:version-print-bugfix into aef9d3a on decebals:master.

[coveralls]

Coverage remained the same at 23.692% when pulling 69601ec on cominvent:version-print-bugfix into aef9d3a on decebals:master.

[decebals]

Thanks!