Upgrade http links to https in Cargo.toml

[Benjins-automation]

This is an automatically-generated PR to update plain HTTP links in Cargo.toml

If there are any issues with this, you can reach out to @/Benjins on Github who is the original author of this automated PR

In file Cargo.toml:

• http://docs.rs/mio-serial was updated. The HTTP version redirects to HTTPS, but does not enforce HSTS