Remove query strings from static resources.

Query strings attached by WordPress to the urls of javascript and css files impact on the Page Speed score.

Thanks to Tricks Machine for this snippet:

Add to your functions.php

function _remove_script_version( $src ){
$parts = explode( '?ver', $src );
return $parts[0];
}
add_filter( 'script_loader_src', '_remove_script_version', 15, 1 );
add_filter( 'style_loader_src', '_remove_script_version', 15, 1 );