Can't login with email 

Hi!

Don't know if I read it wrong on the `README.md`, but I assume `USERNAME` refers to email.
If it does, I was unable to log in using it.

The error is:
`json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)`
As the `data` variable is `b''`.

I am able to login using my API key, though.