Decaffeinate chai.coffee and assertions_spec.coffee.

[sainthkh]

Preparation for #25.

NEVER SQUASH THIS COMMIT.

[cypress-bot]

Thanks for the contribution! Below are some guidelines Cypress uses when doing PR reviews.

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Internal

• The original issue has been tagged with a release in ZenHub.

[jennifer-shehane]

Thanks for the giant text to not squash. I've been saying we need our cypress bot to comment on PRs that have the decaffeinate: in a commit to say not to squash, but...manually handled today.

[cypress-bot]

Released in 3.6.1.