Use a slightly more aggressive backoff approach
Use a slightly more aggressive backoff approach

Doubling the backoff every iteration turned out to be a bit
too relaxed for the common situations where you run into API
throttling. This change gives the API enough room to breathe,
but re-tries requests just a little more often.

178inaba/go-mastodon,mattn/go-mastodon,mattn/go-mastodon