Update microcache_fcgi.conf

See recommendations on:
http://wiki.nginx.org/HttpFastcgiModule#fastcgi_cache_key

fastcgi_cache_key "$scheme$request_method$host$request_uri";
Be advised that a HEAD request can cause an empty response to be cached & later be distributed to GET requests, avoid this by having $request_method in the cache key. Including the $scheme for the same reason may be beneficial to avoid serving up pages with insecure content to HTTPS visitors (or vice-versa).