fix(casks): use postflight_steps

Homebrew rejects a postflight block with Cask/InstallSteps. The four casks now strip the quarantine attribute through postflight_steps. GoReleaser still generates the old block, so the next release of each project writes it back.

Casks/lolcathost.rb

@@ -33,10 +33,9 @@ cask "lolcathost" do
 
   binary "lolcathost"
 
-  postflight do
-    if OS.mac?
-      system_command "/usr/bin/xattr",
-                     args: ["-dr", "com.apple.quarantine", "#{staged_path}/lolcathost"]
+  postflight_steps do
+    on_macos do
+      run "/usr/bin/xattr", args: ["-dr", "com.apple.quarantine", "{{staged_path}}/lolcathost"]
     end
   end