Implement close method in the okhttp HttpResponseImpl to avoid leak

[jcoste-orange]

Fix #855

[vinodborole]

Thanks a lot @jcoste-orange. LGTM, what do you think @auhlig ?

[auhlig]

Nitpicking: We could have saved a couple of characters as response.body().close(); and response.close(); are equivalent.

I guess it's good to merge the way it is now. Thanks @jcoste-orange.

[jcoste-orange]

There's no method close on class okhttp3.Response. So @auhlig I don't understand your comment.

[auhlig]

True. I looked at a newer version of the api. Sorry for the confusion