fix: Duration must be a string. Make it a string.

[foobarbecue]

Missed this when I fixed the docs here: 96af36d

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[foobarbecue]

Actually, wait, don't merge yet -- this happens a few more times in the examples, I'll fix them all.

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[foobarbecue]

Ok, I think this is ready to go. I looked through examples and docs for retryStrategy: duration and just found one more instance of the problem.