Update app to work with new version of Slack apps

[ozovalihasan]

Slack published new Slack apps. The project is updated to work with this version.

Please merge the changes that I did. So, anyone can build an app without any error by using new version of Slack apps.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: ozovalihasan
:x: dependabot[bot]
_{You have signed the CLA already but the status is still pending? Let us recheck it.}