gitahead: add desc, update depends_on, add zap

Casks/g/gitahead.rb

@@ -4,9 +4,16 @@ cask "gitahead" do
 
   url "https://github.com/gitahead/gitahead/releases/download/v#{version}/GitAhead-#{version}.dmg"
   name "GitAhead"
+  desc "Git Client"
   homepage "https://github.com/gitahead/gitahead"
 
-  depends_on macos: ">= :sierra"
+  depends_on macos: ">= :big_sur"
 
   app "GitAhead.app"
+
+  zap trash: [
+    "~/Library/Application Support/GitAhead",
+    "~/Library/Preferences/com.gitahead.GitAhead.plist",
+    "~/Library/Saved Application State/com.gitahead.GitAhead.savedState",
+  ]
 end