Force wordpress embedded content to be https

functions.php

//Add this code to the end of the functions.php file of your wordpress theme
// This forces images urls and links of your website to be displayed with https
function force_https_the_content($content) {
  if ( is_ssl() )
  {
    $content = str_replace( 'src="http://my-domain.tld', 'src="https://my-domain.tld', $content );
	$content = str_replace( 'href="http://my-domain.tld', 'href="https://my-domain.tld', $content );
  }
  return $content;
}
add_filter('the_content', 'force_https_the_content');