Use IP not localhost

The `cors-anywhere` module does some checking against the proxy hostname and it does not consider `localhost` to be valid. This is dumb. To work around this, we replace `localhost` with `127.0.0.1` which matches the `cors-anywhere` validity check for IPv4 addresses.
it's a string, not a regexp. so it does not need to be escaped.

`COOPR_SERVER_URI.replace('/localhost:', '/127.0.0.1:');`