removing final to enable mocking this class

Since this class its hard to instantiate, it should not be final so that we can mock it for testing.

I'm trying to update vraptor-plugin-hibernate4 and we need to mock Parameter class in its tests.

btw, we have two repositories for vraptor-plugin-hibernate4, the one in @garcia-jj and in @caelum, I'm developing in the caelum repo...