function spyfield_auto_embed_tweets($content) {
    $content = preg_replace(
        '/https:\/\/twitter\.com\/([a-zA-Z0-9_]+)\/status\/([0-9]+)/',
        '<blockquote class="twitter-tweet"><a href="$0"></a></blockquote><script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>',
        $content
    );
    return $content;
}
add_filter('the_content', 'spyfield_auto_embed_tweets');