Fix gzip inflation in pipelined HTTP requests

[mendable]

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It appears that pipelined HTTP requests where the response is gzip compressed are not being re-inflated automatically, which net/http can usually handle automatically for non-pipelined requests.

The source of Ruby 2.2 and others has automatic response inflation, but it requires the deflate_content attr-accessor to be set to true in the response instance: https://github.com/ruby/ruby/blob/ruby_2_2/lib/net/http/response.rb#L250

This is set within the Net::GenericRequest by default if the accept-encoding header is going to be turned on for the request: https://github.com/ruby/ruby/blob/ruby_2_2/lib/net/http/generic_request.rb#L36

Could this be merged and a new version of the Gem released please @drbrain ?