Update nginx.conf

Add more gzip_types
https://forum.vestacp.com/viewtopic.php?f=29&t=5100#p20750

install/ubuntu/13.04/nginx/nginx.conf

@@ -51,7 +51,7 @@ http {
     gzip_comp_level     9;
     gzip_min_length     512;
     gzip_buffers        8 64k;
-    gzip_types          text/plain text/css text/javascript
+    gzip_types          text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript image/svg+xml application/x-font-ttf font/opentype;
                         application/x-javascript application/javascript;
     gzip_proxied        any;