Add webp format to assets.conf for Cache Assets

docker/rootfs/etc/nginx/conf.d/include/assets.conf

@@ -1,4 +1,4 @@
-location ~* ^.*\.(css|js|jpe?g|gif|png|woff|eot|ttf|svg|ico|css\.map|js\.map)$ {
+location ~* ^.*\.(css|js|jpe?g|gif|png|webp|woff|eot|ttf|svg|ico|css\.map|js\.map)$ {
 	if_modified_since off;
 
 	# use the public cache