add css version number to WordPress enqued style - Add to functions.php

gistfile1.php

// Adds version to style sheet
// Source - Jason https://wordpress.org/support/topic/add-version-number-to-stylecss-in-custom-theme
function my_wp_default_styles($styles)
{
	//use release date for version
	$styles->default_version = "20130711";
}
add_action("wp_default_styles", "my_wp_default_styles");