Switch to https on iframe creation

external_api.js

         if(height)
             this.iframeHolder.style.height = height + "px";
         this.frameName = "jitsiConferenceFrame" + JitsiMeetExternalAPI.id;
-        this.url = "//" + domain + "/";
+        this.url = "https://" + domain + "/";
         if(room_name)
             this.url += room_name;
         this.url += "#external=true";