[patch] fix data type in docs (should be optional)

[mikermcneil]

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[sailsbot]

Hi @mikermcneil! It looks like the title of your pull request doesn’t quite match our guidelines yet. Would you please edit your pull request's title so that it begins with [proposal], [patch], [fixes #<issue number>], [implements #<other PR number>], or [misc]? Once you've edited it, I'll take another look!

[sailsbot]

Thanks for submitting this pull request, @mikermcneil! We'll look at it ASAP.

In the mean time, here are some ways you can help speed things along:

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