Update js-yaml calls in docgen script

[hsubox76]

Updated js-yaml dependency has some API changes.

[changeset-bot]

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Latest commit: d519268

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[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (c49689b) and head commit (0e2c078).

Test Logs

• Base (c49689b1): https://github.com/firebase/firebase-js-sdk/actions/runs/641928923
• Head (0e2c0789): https://github.com/firebase/firebase-js-sdk/actions/runs/643549222

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (c49689b) and head commit (0e2c078).

Test Logs

• Base (c49689b): https://github.com/firebase/firebase-js-sdk/actions/runs/641928923
• Head (0e2c078): https://github.com/firebase/firebase-js-sdk/actions/runs/643549222