How to release new version

Update CHANGELOG.md
Upgrade version of metadata.rb
git commit -m "Bump version x.x.x"
git tag vx.x.x
git push origin master && git push --tags
Check CI status at https://travis-ci.org/mackerelio/cookbook-mackerel-agent
bundle exec stove --no-git --username mackerel --key /path/to/pem. See https://supermarket.chef.io/cookbooks/mackerel-agent