Update rewrite rule for CSS Cheat Sheet from alias to permanent redirect

Author: Fechin

Diff for: nginx.conf

@@ -34,11 +34,7 @@ http {
 
         # Rename cheatsheet
         rewrite ^/golang$ /go permanent;
-
-        # Resolve CSS Cheat Sheet and CSS style directory conflict.
-        location ^/css$ {
-            alias css.html;
-        }
+        rewrite ^/css$ /css3 permanent;
 
         location / {
             try_files $uri $uri/ @html;