Revert "[pkg/token]: Update credential API version"

[wongma7]

This reverts commit 0221afb.

See #440, this should not have been released in a patch release. Let's revert, make a 0.5.6, and then release 1.x.x (and maintain a 0.5.x branch if necessary).

(context: i updated authenticator today and encountered same issue as #440)

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Test name	Commit	Details	Required	Rerun command
pull-aws-iam-authenticator-integration	7259113	link	true	/test pull-aws-iam-authenticator-integration

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[wongma7]

closing in favor of #439, actually #439 to support both alpha and beta will be less effort then this which i thought would be a simple revert : (