Arduino only sends HTTP 1.0 requests
The device sending the request has no bearing on if it is HTTP 1.0 or 1.1. Only the content has an effect.

That and what is in the path - and I suspect that may be your problem: your are going through a squid proxy - and an old version at that. It is most likely that the proxy is changing the request to be a 1.0 request instead of a 1.1 request.