Typo in extra gateway instructions

`service.beta.kubernetes.io/aws-load-balancer-internal: "true`

Need a quote on the end to fix a typo.

!48 (merged) Should have taken care of this typo. This is a annotation for the Ingress Gateways. By default it will be commented out, but left in place as an example. In addition, please scrub the documentation to see if this appears in there.