Request is not repeated when 502-503 or 429 response received

[tvims81]

Issue may be related with #36

In version 0.13.1 if 502, 503 or 429 response status is received by dshackle from upstream, request is not repeated as it described in docs here
https://github.com/emeraldpay/dshackle/blob/master/docs/04-upstream-config.adoc#roles-and-fallback-upstream

In version 0.13.0 if 502 error is received by dshackle, it seems request is to be repeated, further normal upstream response passed to the initial client's request. With 503 or 429 error statuses from upstream the situation is the same as in the 0.13.1.