Ensure http.Response.Body is closed

[Integralist]

Fixes #362

[doramatadora]

Surprisingly easy to review — 1 change in many places :)

[joeshaw]

No objection here, but decodeBodyMap already closes the body and it looks like almost all (if not all) requests call that:

go-fastly/fastly/client.go

Line 471 in fedbcfc

defer body.Close()

That makes me wonder if the leak was somewhere else, or if there were particular calls that weren't closing the body.

And it means that the defer body.Close() can probably be dropped from decodeBodyMap and it can take an io.Reader instead of an io.ReadCloser.

[Integralist]

Damn, I didn't realise it was in the decodeBodyMap. My bad. I'll open another PR to fix this up and remove from decodeBodyMap as you've suggested.