Enabled AWS managed policy.

[otakumesi]

What did you implement:

Enable AWS managed policy.

https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies_managed-vs-inline.html#aws-managed-policies

How did you implement it:

AWS managed policy's ARN format is arn:aws:iam::aws:policy/{{ROLE_NAME}}. But, This format is ServerlessPlugin#verifyConfig() is not acceptable. So, I touch up.

[erikerikson]

Thanks for this @otakumesi.

Looks good to me at a glance but I'll defer to @gwsii for the merge and publish.

[gwsii]

mergeは日本語で何ですか。知らない。でも僕たちわします。ありがとう！

[otakumesi]

@erikerikson @gwsii Thank you, too!!!

Japanese software developers also call "merge" merge. So, "merge" make sense.