Typo: insert omitted 'function' keyword

[bmusin]

Yes, I promise I've read the Contributions Guidelines (please feel free to remove this line).

Specifically quoting these guidelines regarding typos:

Typos?

Please don't worry about minor text typos. These will almost certainly be caught during the editing process.

If you're going to submit a PR for typo fixes, please be measured in doing so by collecting several small changes into a single PR (in separate commits). Or, just don't even worry about them for now, because we'll get to them later. I promise.

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[getify]

Thanks!