Focus slack window and next unread conversation

slack.applescript

activate application "Slack"
tell application "System Events" to tell process "Slack"
  key code 125 using {option down, shift down}
end tell
-- use with FastScripts - http://www.red-sweater.com/fastscripts/
-- FastScripts pauses script execution before key presses until
-- you've released the hotkey meta character. This makes it more 
-- reliable than just running it as a Service via a shortcut in
-- System Preferences.