nginx: bump lua module to fix build error (https://github.com/openresty/lua-nginx-module/pull/500)

pkgs/servers/http/nginx/unstable.nix

···
   lua-ext = fetchFromGitHub {
     owner = "openresty";
     repo = "lua-nginx-module";
-    rev = "v0.9.12";
-    sha256 = "0r07q1n3nvi7m3l8zk7nfk0z9kjhqknav61ys9lshh2ylsmz1lf4";
+    rev = "v0.9.16";
+    sha256 = "0dvdam228jhsrayb22ishljdkgib08bakh8ygn84sq0c2xbidzlp";
   };
 
 in