Slack 4.15.0

Previously, clicking on a notification in Windows Action Center didn't bring you to the message in Slack — basically the opposite of walking into a room and forgetting what you came for, but no less confusing. Sometimes when the Windows app was launching, it instead decided to hit the Snooze button and just hang there for a while. We gave it a polite talking-to, and it will now be more punctual. This release includes minor security improvements. Updating is beneficial.