Convert shortcode to AMP compatible Shortcode

function.php

<?php
// Do not copy the above php tag in your function.php
/**
 * Change shortcodes to AMP compatible Shortcodes
 *
 * Add this to your function.php
 *
 * @author  MetaBlogue
 * @license GPL-2.0+
 * @link    https://metablogue.com/configure-enable-amp-wordpress/ 
 */
add_shortcode('gist-amp', 'jetpack_gist_amp_conversion');
function jetpack_gist_amp_conversion( $atts, $content = NULL ) {
	if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
		$amp_gist_string = '<amp-gist layout="fixed-height" height="225" data-gistid="' .$content. '">' . '</amp-gist><br />';
		return $amp_gist_string;
	} else {
		return do_shortcode('[gist]' .$content .'[/gist]');
	}
}