kill yarn, bump to node 8

[arizzitano]

Description

TODO: Link to a JIRA ticket if one has been created for this feature/issue.
Use the following format for a link: [FEDX-100](https://openedx.atlassian.net/browse/FEDX-100)

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Manual Test Plan

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Testing Checklist

• Write unit tests for all new features.
• Write accessibility (a11y) tests for all new UI.
• Manually test responsive behavior.

Non-testing Checklist

• Consider any documentation your change might need, and which users will be affected by this change.
• Consult with the Pattern Library team if adding a new component.

Post-review

• Squash commits into discrete sets of changes with descriptive commit messages.

Reviewers

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[coveralls]

Coverage remained the same at 98.848% when pulling 8efb252 on ari/node-8 into 1863983 on master.

[coveralls]

Coverage remained the same at 98.848% when pulling 7cfde53 on ari/node-8 into 1863983 on master.

[coveralls]

Coverage remained the same at 98.848% when pulling aad196f on ari/node-8 into 1863983 on master.

[yro]

@arizzitano 🚢

[bjacobel]

😭

[arizzitano]