Merge pull request #299 from nodejsjp/yosuke-furukawa-patch-1

Update contact.md

Author: yosuke-furukawa

source/contact.md

@@ -3,7 +3,7 @@
 ---
 
 ## Slack
-- 未登録の方: [https://iojs-jp-slack.herokuapp.com](https://iojs-jp-slack.herokuapp.com)
+- 未登録の方: [jsconf.jp invite link](https://join.slack.com/t/jsconfjp/shared_invite/zt-1j7fqgvbq-Qa334TtwwKWC1eJBrgJ3yQ)
 - 登録済みの方: [https://iojs-jp.slack.com](https://iojs-jp.slack.com)
 
 ## IRC