does not handle bucket names with periods

[michalkrupa]

issue with using the bucket cdn.example.com, but cdn_example works. I am using imager and S3 which utilizes knox, and first I thought that it was an imager issue but I believe it breaks when imager.js trades off the configuration file to:

var client = knox.createClient(s3Config);

I have also opened an issue with Knox.js

[madhums]

I have added this in gotchas in the readme. This is a known issue Automattic/knox#125