Cross browser handling of retrying on network connection issues

[peterj35]

Based on this issue, p-retry now can be used to retry based on network errors on Chrome. Nice!

However, as mentioned in the 'slightly relevant ' fetch issue, different browsers have different messages based on the network errors:
Chrome: TypeError: Failed to fetch
Firefox: TypeError: NetworkError when attempting to fetch resource.
Safari: TypeError: The Internet connection appears to be offline.
(source)

Would it be possible to support network errors in Firefox and Safari, and also retry on them -- also happy to put in a PR by referencing https://github.com/sindresorhus/p-retry/pull/38/files.