How to convert a HEIF/HEIC image to JPEG in macOS?

So, here’s the thing. I have a new iPhone and an old Mac. iOS 11 (still in beta as of today) and El Capitan (no more updates for this Mac). I use iCloud photo library in both devices. When I take a photo in the new format with my iPhone 7, is there any way to use it right away in my mac, without having to convert it in my iPhone first? I mean, can I get those photos synced through iCloud and converted locally on my Mac? I have tried to find a third party software that could do that kind of conversion, but was not able to find any that would work on El Capitan. Any idea?