MIME: added image/avif type.

Prodded by Ryo Hirafuji, André Rømcke, Artur Juraszek.

conf/mime.types

diff --git a/conf/mime.types b/conf/mime.types
index b53f7f7..1c00d70 100644
--- a/conf/mime.types
+++ b/conf/mime.types
@@ -15,6 +15,7 @@
     text/vnd.wap.wml                                 wml;
     text/x-component                                 htc;
 
+    image/avif                                       avif;
     image/png                                        png;
     image/svg+xml                                    svg svgz;
     image/tiff                                       tif tiff;