aws-appsync-auth-link 4 next with new apollo

Hi,

I've been trying to use the new aws-appsync-auth-link and aws-appsync-subscription-link ^4 with the new version of Apollo and it breaks auth with AWS_IAM.

This is due to the new version of HttpLink in Apollo with adds automatically: new ClientAwarenessLink(options). It changes the payload after being signed.

to make it work, use directly BaseHttpLink instead.

