buildbot failure in on sling-site-staging

[buildbot]

The Buildbot has detected a new failure on builder sling-site-staging while 
building . Full details are available at:
    https://ci.apache.org/builders/sling-site-staging/builds/537

Buildbot URL: https://ci.apache.org/

Buildslave for this Build: bb-cms-slave

Build Reason: The AnyBranchScheduler scheduler named 'on-sling-site-commit' 
triggered this build
Build Source Stamp: [branch sling/site] 1771824
Blamelist: rombert

BUILD FAILED: failed shell

Sincerely,
 -The Buildbot