Update triggers.md

[NatalieNobile]

Description

triggers.md lists incorrect trigger values for docgen triggers.

It lists DOCGEN_DOCUMENT_GENERATION_FAILED, DOCGEN_DOCUMENT_GENERATION_STARTED, and DOCGEN_DOCUMENT_GENERATION_SUCCEEDED.

Those don't work. DOCGEN_DOCUMENT_GENERATION.FAILED, DOCGEN_DOCUMENT_GENERATION.STARTED, and DOCGEN_DOCUMENT_GENERATION.SUCCEEDED do work. (tested via API)

This branch updates to correct format.

If you are a Boxer, please also reference the related DDOC or APIWG tickets.
If you do not have a related Jira ticket and this is more than a bug fix, then
create one now.

Fixes # (issue)
Re DDOC-1643

Checklist

• [y ] My code follows the style guidelines of this project
• [y ] I have performed a self-review of my own changes
• [ n] I have run yarn lint to make sure my changes pass all linters
• [ y] I have pulled the latest changes from the upstream developer branch

Contribution guidelines

For contribution guidelines, styleguide, and other helpful information please
see the CONTRIBUTING.md file in the root of this project.

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[mwwoda]

Thanks a lot for fixing this! It already helped to close box/box-windows-sdk-v2#1457