added HSTS header to database

Many sites started to implement [HTTP Strict Transport Security][1], but Nikto reports it as the following:

    + Uncommon header 'strict-transport-security' found, with contents: max-age=31536000; includeSubDomains

I added the HTTP header to the appropriate database file, which silences this false positive.

  [1]: https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security