_set_api_key_parameter() doesn't work

[ofer-pd]

The README demonstrates calling _set_api_key_parameter() with an API key, but if you follow the path of execution through the code, you'll see that argument never gets saved and used.

Furthermore, if you add a print statement to _query_cryptocompare() to dump the URL before issuing a request, you can see the param isn't being added.

I'd be happy to fix it if this project is still active enough to accept and merge PRs.