fix for robots.txt location

Allow wordpress to generate robots.txt file if static file does not exist

config/nginx/common/locations.conf

@@ -9,6 +9,7 @@ location = /favicon.ico {
 }
 
 location = /robots.txt {
+		try_files $uri $uri/ /index.php?$args;
 		access_log off;
 		log_not_found off;
 }