fix the issue that tick tuple cannot work with system bolt
Do the worker HB timeout check when HB's are updated
Merge pull request #706 from d2r/d2r-nimbus-hb-check-timeout-on-update

Do the worker HB timeout check when HB's are updated
Merge pull request #702 from xumingming/fix-system-bolt

fix the issue that tick tuple cannot work with system bolt
Update README.md with list of Apache committers (#721)
update README.md with Apache mailing list info
fix typo in the dev subscribe links
fix typos