PmdPlugin JavaDoc fix

Removed findbugs references from PmdPlugin. This was fairly straightforward with the exception of this line: 'Additional plugins can be added to the <tt>findbugsPlugins</tt> configuration'.

There does not appear to be an equivalent configuration for the PmdPlugin, so I removed that line. Please let me know if I'm wrong there. Other than that this is very nearly s/findbugs/pmd/i.

Thanks!