Fix for uninitialized constant OpenSSL

This patch is a fix that `NameError` was raised when this client connect to a GrowthForecast server.

In terminal:

```
$ ruby -v
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux]
$ ruby -rgrowthforecast-client -e 'GrowthForecast::Client.new("http://localhost:5125").list_section'
/home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:45:in `block in http_connection': uninitialized constant GrowthForecast::Client::OpenSSL (NameError)
        from /home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:41:in `tap'
        from /home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:41:in `http_connection'
        from /home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:81:in `get_json'
        from /home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:128:in `list_graph'
        from /home/kui/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/growthforecast-client-0.82.4/lib/growthforecast/client.rb:149:in `list_section'
        from -e:1:in `<main>'
```