Non-static method MS_Rule_Shortcode_Model::debug_protect_content_shortcode() called statically

Hi!

I'd like to report a bug: Membership 2 Pro is throwing a PHP Depricated error: Non-static method MS_Rule_Shortcode_Model::debug_protect_content_shortcode() should not be called statically.

I've been able to trace it back to the fact that debug_protect_content_shortcode on line 261 in the file "plugins/membership/app/rule/shortcode/class-ms-rule-shortcode-model.php" is not defined as being static. Thus the error. So either the method should be defined as static, or the way it is being called should be changed.

Thoughts?