Updating mvn plugin versions.

[Rod Widdowson]

> I'll be doing this tomorrow morning.  People may have seen from the svn
log that I did this and backed it off when java-support went unstable in
Jenkins

I finally traced this to a problem with cobatura and so I skipped that
update and all is good.

The lesson from this (for me at least) is that running 'mvn install' isn't
necessarily sufficient when making these sorts of changes, you need to run
'mvn site'.

I have amended the wiki appropriately.