force yarn as package manager

[gflohr]

What?

Allow upgrading a PDF document to PDF/A.

Why?

See #98

How?

The conversion process makes the necessary modifications to a PDF document.

Testing?

Unit tests are used for black-box testing. Locally, VeraPDF is used to test conformance with PDF/A.

New Dependencies?

No

Screenshots

N/A

Suggested Reading?

No

Anything Else?

N/A

Checklist

• I read CONTRIBUTING.md.
• I read MAINTAINERSHIP.md#pull-requests.
• I added/updated unit tests for my changes.
• I added/updated integration tests for my changes.
• I ran the integration tests.
• I tested my changes in Node, Deno, and the browser.
• I viewed documents produced with my changes in Adobe Acrobat, Foxit Reader, Firefox, and Chrome.
• I added/updated doc comments for any new/modified public APIs.
• My changes work for both new and existing PDF files.
• I ran the linter on my changes.

[gflohr]

Sorry, I messed up. This was meant for my own fork.