only cache 200 response code pages

to keep fastcgi cache from mistakenly caching (and then serving) 5XX error pages and other things it shouldn't, only cache pages with a 200 response code.

config/nginx/conf.d/fastcgi.conf

@@ -3,7 +3,7 @@
 fastcgi_cache_path /var/run/nginx-cache levels=1:2 keys_zone=WORDPRESS:50m inactive=60m;
 fastcgi_cache_key "$scheme$request_method$host$request_uri";
 fastcgi_cache_use_stale error timeout invalid_header updating http_500 http_503;
-fastcgi_cache_valid any 1h;
+fastcgi_cache_valid 200 1h;
 
 fastcgi_buffers 16 16k;
 fastcgi_buffer_size 32k;