def upgrade_scheme(url):
    """
    Upgrade crawled scheme to https, if reasonable. This helps to reduce MITM attacks against the crawler.

    https://chromium.googlesource.com/chromium/src/net/+/master/http/transport_security_state_static.json

    Alternately, the return headers from a site might have strict-transport-security set ... a bit more
    dangerous as we'd have to respect the timeout to avoid permanently learning something that's broken

    TODO: use HTTPSEverwhere? would have to have a fallback if https failed, which it occasionally will
    """
    return url
