Merge pull request #3 from lazyppp/support_deploy_status

Support deploy status
upgrade slack-notifier to 1.0.0
Merge pull request #5 from exherb/update-slack-notify

upgrade slack-notifier to 1.0.0
Change webhook to webhook_url for understandability
Support channel override
Small fix for README
Bump up version to 0.2.2
Merge pull request #6 from wantedly/support-channel-override

Support channel override