Site speed issues spotted with GMetrix (Vary: Accept-Encoding Header)

Hi guys,

not sure if this is the right place to ask this, but I just ran a GMetrix test for one of my pages and got a score of 60%

I got an F on this: Specify a Vary: Accept-Encoding header

The solution I found was to add this in .htaccess:
<IfModule mod_headers.c>
<FilesMatch ".(js|css|xml|gz|html)$">
Header append Vary: Accept-Encoding
</FilesMatch>
</IfModule>

When I try to run the test again, GMetrix tells me exactly the same...

Site speed issues spotted with GMetrix (Vary: Accept-Encoding Header)

from Search Engine Optimization http://bit.ly/2JqWfmp
via IFTTT