Fix unresolvable dependency of stapler 1.208-SNAPSHOT

Update stapler from 1.208-SNAPSHOT to 1.209 to fix Maven build of java-runtime.

I skipped stapler 1.208(-SNAPSHOT)? since it seems to not deployed to http://repo.jenkins-ci.org by the problem of Maven configuration at stapler/stapler@03c56ad8c976083d9526f56a21640e6b0c0bc14b