switch to nixpkgs slack instead of homebrew

modules/darwin/hammerspoon/Spoons/Launcher.spoon/init.lua

@@ -93,7 +93,7 @@ function obj:init()
         hs.reload()
     end)
     self.launcher:bind("", "S", function()
-        self:switch("Slack.app")
+        self:switch("@slack@")
     end)
     self.launcher:bind("", "Z", function()
         self:switch("zoom.us.app")