Pin CDN version of GraphiQL to 3.x

[JPrevost]

4.x recently was released and breaks our GraphiQL playground.

https://mitlibraries.atlassian.net/browse/TCO-166 is tracking how to upgrade to v4

Summary of changes (please refer to commit messages for full details)

Developer

Ticket(s)

https://mitlibraries.atlassian.net/browse/TCO-###

Accessibility

• ANDI or Wave has been run in accordance to our guide and
  all issues introduced by these changes have been resolved or opened
  as new issues (link to those issues in the Pull Request details above)
• There are no accessibility implications to this change

Documentation

• Project documentation has been updated, and yard output previewed
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ENV

• All new ENV is documented in README.
• All new ENV has been added to Heroku Pipeline, Staging and Prod.
• ENV has not changed.

Stakeholders

• Stakeholder approval has been confirmed
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Dependencies and migrations

NO dependencies are updated

NO migrations are included

Reviewer

Code

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  added technical debt.

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  (not just this pull request message).
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• New dependencies are appropriate or there were no changes.

Testing

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