Gets a random Reddit post.

    Syntax: {command} [subreddit]

def cmd(send, msg, args):
    """Gets a random Reddit post.

    Syntax: {command} [subreddit]

    """
    if msg and not check_exists(msg):
        send("Non-existant subreddit.")
        return
    subreddit = msg if msg else None
    send(random_post(subreddit, args['config']['api']['bitlykey']))