Require Chromium >=60

Background

Apparently any version of Chrome < 60 throws file errors when extensions are installed from the Web Store.

I'm not sure they changed the minimal required Chrome version (and btw, 59 is the version that updates itself automatically to the latest), but 55, 58, and 59 throw file erros, while 60 gets the extension installed.

The issue is not just with ABP, it's every extension I could try.

What to change

Increase minimum_chrome_version in manifest.json to 60, and respectively minimum_opera_version to 47.