Add .webp to supported lightbox images (mmistakes#2788)

Author: rlaphoenix

assets/js/_main.js

@@ -83,7 +83,7 @@ $(document).ready(function() {
 
   // add lightbox class to all image links
   $(
-    "a[href$='.jpg'],a[href$='.jpeg'],a[href$='.JPG'],a[href$='.png'],a[href$='.gif']"
+    "a[href$='.jpg'],a[href$='.jpeg'],a[href$='.JPG'],a[href$='.png'],a[href$='.gif'],a[href$='.webp']"
   ).addClass("image-popup");
 
   // Magnific-Popup options