bump maven-war-plugin version (old version was fine here but new version...

... needed in downstream projects),

along with the parameter which fixes the second copy overwriting the files changed by the replacer plugin (for war plugin v 2.1+); confirmed the resulting WAR is identical apart from the pom changes

[this was reviewed and merged by @aledsage in to the old brooklyncentral/brooklyn but the commit did not get moved across to apache]