Allow `faraday-net_http` up to v3.1
Allow `faraday-net_http` up to v3.1

Version 3.0 of `faraday-net_http` uses the new streaming API and the new `finished` option in `save_response`, which are not available in `faraday` prior to version 2.5, and has therefore been released as a new major version.

To avoid the same issue in future, we're fixing the version to allow any 3.0.x version, but not 3.1+.
This will allow us to ship a minor versions of the adapter with "breaking" changes for older versions of Faraday.

lostisland/faraday,lostisland/faraday