Updating helix to 0.6.2-incubating because of HELIX-257

See:     
- [HELIX-257](https://issues.apache.org/jira/browse/HELIX-257)
- [0.6.2-incubating release notes](http://helix.incubator.apache.org/releasenotes/release-0.6.2-incubating.html)