use correct syntax for more_set_headers

src/nginx/common.conf

@@ -80,7 +80,7 @@ location ~ /\.  { access_log off; log_not_found off; deny all; }
 
 # for user uploaded files, use a long cache value, as uploads are not modified anyway: an URL points always to the same exact file
 location ^~ /app/download.php {
-    more_set_headers Cache-Control "public, max-age=31536000";
+    more_set_headers "Cache-Control: public, max-age=31536000";
     include         /etc/nginx/fastcgi.conf;
     fastcgi_index  index.php;
     log_not_found off;