Always Fresh Editor_style in TinyMCE WYSIWYG

fresh_editor_style.php

<?php 
add_filter( 'mce_css', 'lm_fresh_editor_style' );

/**
 * Adds a parameter of the last modified time to all editor stylesheets.
 *
 * @wp-hook mce_css
 * @param  string $css Comma separated stylesheet URIs.
 * @return string $css Comma separated stylesheet URIs with version timestamp.
 */
function lm_fresh_editor_style( $css ) {
	global $editor_styles;

	if ( empty( $css ) or empty( $editor_styles ) ) {
		return $css;
	}

	// Modified copy of _WP_Editors::editor_settings()
	$mce_css   = array();
	$style_uri = get_stylesheet_directory_uri();
	$style_dir = get_stylesheet_directory();

	if ( is_child_theme() ) {
		$template_uri = get_template_directory_uri();
		$template_dir = get_template_directory();

		foreach ( $editor_styles as $file ) {
			if ( $file && file_exists( "$template_dir/$file" ) ) {
				$mce_css[] = add_query_arg(
					'version',
					filemtime( "$template_dir/$file" ),
					"$template_uri/$file"
				);
			}
		}
	}

	foreach ( $editor_styles as $file ) {
		if ( $file && file_exists( "$style_dir/$file" ) ) {
			$mce_css[] = add_query_arg(
				'version',
				filemtime( "$style_dir/$file" ),
				"$style_uri/$file"
			);
		}
	}

	return implode( ',', $mce_css );
}