Fixed failed spec
Fixed failed spec

faraday is sending all values as strings

```
  1) ChatWork::Task.create when to_ids and limit are String behaves like a_chatwork_api
     Failure/Error: response = @conn.__send__(method, @api_version + url, *args)

     WebMock::NetConnectNotAllowedError:
       Real HTTP connections are disabled. Unregistered request: POST https://api.chatwork.com/v2/rooms/123/tasks with body 'body=Buy+milk&limit=1385996399&to_ids=1%2C3%2C6' with headers {'Accept'=>'*/*', 'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3', 'Content-Type'=>'application/x-www-form-urlencoded', 'User-Agent'=>'ChatWork/v2 RubyBinding/0.6.0', 'X-Chatworktoken'=>'api_key'}

       You can stub this request with the following snippet:

       stub_request(:post, "https://api.chatwork.com/v2/rooms/123/tasks").
         with(body: {"body"=>"Buy milk", "limit"=>"1385996399", "to_ids"=>"1,3,6"},
              headers: {'Accept'=>'*/*', 'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3', 'Content-Type'=>'application/x-www-form-urlencoded', 'User-Agent'=>'ChatWork/v2 RubyBinding/0.6.0', 'X-Chatworktoken'=>'api_key'}).
         to_return(status: 200, body: "", headers: {})

       registered request stubs:

       stub_request(:post, "https://api.chatwork.com/v2/rooms/123/tasks").
         with(body: {"body"=>"Buy milk", "limit"=>1385996399, "to_ids"=>"1,3,6"},
              headers: {'Content-Type'=>'application/x-www-form-urlencoded', 'X-Chatworktoken'=>'api_key'})

       ============================================================
```

asonas/chatwork-ruby,asonas/chatwork-ruby