Fix "type 'Response' is not a subtype of type 'StreamedResponse' in type cast" after retrying a request

[KacperKluka]

Issue description:
When you use the library in version 2.0.0 and create theInterceptedClient with a retryPolicy and then call the send() method it throws a "type 'Response' is not a subtype of type 'StreamedResponse' in type cast" exception after the retryPolicy was used to retry the request.

Proposed fix:
After #132 the _attemptRequest() method has received an optional parameter isStream set by default to false. When the retryPolicy is invoked inside the method, the _attemptRequest() is recursively called again but the isStream parameter isn't passed through, but rather the default value is being used. Due to that even if you call _attemptRequest(isStream: true) then after using retryPolicy it will be called again but with the default value false, which then leads to the type cast error.

Hopefully, it could possibly fix the #134 if it isn't resolved already 😉

[grAPPfruit]

We have the same problem and are waiting for this fix to get merged.
Please get to it <3

[KacperKluka]

@CodingAleCR could you please find some time to look at the fix and include it in the next release? 🙇 Thanks! ❤️