/__reload route does not use custom headers

[cboitel]

When starting apisprout --header "CustomerHeader: value" uri, apisprout will as expected load the swagger definition at uri provided using the custom header provided. We use it to provide a security access token to access the protected uri resource.

When asking apisprout to reload the definition via a /__reload call:

• custom header won't be used
• download will fail (our server reports a 404 if our security heaser isn't sent)
• apisprout will display 'Reloaded from uri" message and no error is reported
• apisprout won't fail and will keep on working assuming an empty definition has been provided (all calls to apisprout will result in 404)

Will try to provide a fix via a PR.