nginx: add more gzipped MIME types

The additions are:

 - image/svg+xml for SVG images
 - application/atom+xml for Atom feeds

These types are also present in mime.types. For better readability,
the list is sorted and formatted with one type per line.

nixos/modules/services/web-servers/nginx/default.nix

@@ -93,7 +93,17 @@ let
         gzip_disable "msie6";
         gzip_proxied any;
         gzip_comp_level 5;
-        gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
+        gzip_types
+          application/atom+xml
+          application/javascript
+          application/json
+          application/xml
+          application/xml+rss
+          image/svg+xml
+          text/css
+          text/javascript
+          text/plain
+          text/xml;
         gzip_vary on;
       ''}