Set connection.keep_alive_timeout using idle_timeout in ruby 2.0.

Ruby 2.0 added keep_alive_timeout, which behaves the same way as
idle_timeout, except that the default timeout is 5 seconds rather than 2
seconds. Set keep_alive_timeout using idle_timeout to prevent the
connection from getting closed before idle_timeout due to delays between
requests.
Merge pull request #53 from dylanahsmith/keep-alive-timeout

Set connection.keep_alive_timeout using idle_timeout in ruby 2.0.