fix missing response.Body.Close()

[brenol]

As mentioned in Do docs:

// If the returned error is nil, the Response will contain a non-nil
// Body which the user is expected to close. If the Body is not both
// read to EOF and closed, the Client's underlying RoundTripper
// (typically Transport) may not be able to re-use a persistent TCP
// connection to the server for a subsequent "keep-alive" request.

I also thought of changing from your custom HttpClient interface to the default http.RoundTripper interface. What do you think?

[TwiN]

I also thought of changing from your custom HttpClient interface to the default http.RoundTripper interface. What do you think?
@brenol The only reason I'm using a custom HttpClient is so I can mock it. As long as the change you're suggesting doesn't affect the ability to mock responses, I'm fine with it.

Thank you for the contribution!

[TwiN]

Released in v0.0.2