Let preview URL use HTTP

Hello,

Firstly, thanks for creating this plugin. I can't thank you enough for this plugin.

Currently, previewing a post is shown in HTTPS. However, this results in unwanted scenarios, such as, mixed content errors. To avoid it, let previewing happen only via HTTP.

Please feel free to correct / improve it, if you wish. If you have any questions, please reply back.

Thanks again,
Pothi