Retrospective changes on time limit are shared via Slack even if Notify the team via Slack checkbox isn't checked

[rafaelromcar-parabol]

Issue - Bug

• How serious is the bug? P4
• OS: macOS / Linux / Windows / ?
• Browser: Chrome / Safari / Lynx / ? + version
• Node version: node --version
• NPM version: npm --version
• RethinkDB version: rethinkdb --version

I created a retrospective and I then set a time limit. Then I changed my mind (twice) and changed that time limit without checking the checkbox "Notify team via Slack", but Parabol shared that change via Slack anyway, both times.

Acceptance Criteria (optional)

Changes on the retrospective time limit are not shared via Slack when the checkbox isn't checked.
Triage is performed to find the root cause of the bug, timeboxed to ~1 hour.

Estimated effort: 1 hour to triage. More if root cause is already identified.