No SSL support

When using this plugin on a SSL enabled website I get a “security risk” error in browser. Because ..

<div style="text-align:left; padding: 0; margin: 0; background: url(https://www.domain.tld/wp-content/plugins/gd-star-rating/stars/oxygen/stars12.png); height: 12px; width: 120px;"><div style="background: url(https://www.domain.tld/wp-content/plugins/gd-star-rating/stars/oxygen/stars12.png) bottom left; padding: 0; margin: 0; height: 12px; width: 117.6px;"></div></div>

The domain is set in General Settings to https://www.domain.tld/ and SSL cert is OK.