EKS ami policy fails legacy parsing with MalformedPolicyDocument error

Hi there,

I've followed the instructions in `installation.md` up to the `Create IAM Policy` step. Unfortunately I get the following error:

```
~/torchserve-eks$ aws iam create-policy --policy-name eks_ami_policy \
--policy-document file://eks_ami_policy.json
>
An error occurred (MalformedPolicyDocument) when calling the CreatePolicy operation: The policy failed legacy parsing
```

The error seems to suggest the `eks_ami_policy.json` (templated here: https://github.com/aws-samples/torchserve-eks/blob/master/template/eks_ami_policy.json) generated by `pt_serve_util.sh` is faulty.

Looking at the `eks_ami_policy.json` generated by `pt_serve_util.sh`, it appears to match the template exactly. So I'm not sure how it is that has failed legacy parsing.