add X-Content-Type-Options nosniff

Add from https://github.com/RaymiiOrg/raymiiorg.github.io/blob/244fec3596d731823ed072f295be2521984b24ec/tutorials/Strong_SSL_Security_On_nginx.html.

`add X-Content-Type-Options nosniff`
> The script and styleSheet elements will reject responses with incorrect MIME types if the server sends the response header "X-Content-Type-Options: nosniff". This is a security feature that helps prevent attacks based on MIME-type confusion.