Both your OS and Safari are out of date compared to mine.
The following would work in my opinion - and what I have in mind is that devs who are going to use Butler are not afraid of Terminal. So why use Safari in the first place?
- Provide a cut-and-paste command that would download (and if possible install) Butler.
- Provide a homebrew installer (I'm fixing a brew install for something right now so I might be able to help after I'm done and get a bit more familiar with this.