Ruby 2: Added Testing for Heroku::Conn#parse_body

Net::HTTP#request does not automatically perform gzip reading any more
for some reason, so I am dealing with encoding at this level to fix
this. (Net::HTTP#get *does* however decompress the body)
Ruby 2: Implementing Heroku::Conn.parse_body

See previous commit for motivation. (Fix for change in Ruby 2 from
Ruby 1.9)