Fix HTTP.rb non-ascii URI parsing

[stephannv]

When Appsignal is enabled, it hooks into HTTP request method. It uses URI.parse when uri is a string, but URI.parse doesn't support non-ascii characters:

HTTP.get("http://www.example.com/áéíóúãÔù") # it works when appsignal is disabled

With Appsignal enabled, the code above raises this error:

URI::InvalidURIError:
       URI must be ascii only "http://www.example.com/\u00E1\u00E9\u00ED\u00F3\u00FA\u00E3\u00D4\u00F9"

The solution I found was using Addressable::URI.parse since it handles non-ascii characters.

ps.: Addressable is a HTTP's runtime dependency since 2015

[unflxw]

Thanks for fixing this issue @stephannv! I've made some minor tweaks to it in #1370 -- continuing there.