Update Italian messages

[shgysk8zer0]

Update _locales/it/messages.json.

The full list of messages may be found in _locales/en/messages.json

Awesome RSS is about to surpass 5,000 daily users, and I would really like to have the add-on localized for the most common languages so that it's more friendly to the majority of users. I do not trust Google Translate for the job, and am asking users for help with this.

If you are willing to help, it only requires some copy/pasting and working in a JSON file. To see all open issues requesting translations, look through issues with the translations label. For all issues requesting help, there is also a "help wanted" label and a "good first issue" label

Please create/update the appropriate locale, matching the English version, and submit a pull request referencing the issue. Other languages are, of course, always welcome.

[ziriuz84]

Just made