Revert "roles/nginx: Correct HSTS header in https template"

This reverts commit 5c7404d228.

'always' is legal in nginx >= 1.7.5:

If the always parameter is specified (1.7.5), the header field will be added regardless of the response code.

See: http://nginx.org/en/docs/http/ngx_http_headers_module.html

roles/nginx/templates/https.j2

@@ -35,5 +35,5 @@
     spdy_headers_comp 6;
 
     # Enable this if you want HSTS (recommended, but be careful)
-    add_header Strict-Transport-Security max-age=15768000;
+    add_header Strict-Transport-Security max-age=15768000 always;