Set up React 16 Enzyme adapter for tests (#149)
Set up React 16 Enzyme adapter for tests (#149)

## Summary:

We still have a few enzyme tests in our codebase. In the near future we'll migrate them (LP-11633), but for now it's relatively easy to get them passing.

Issue: "none"

## Test plan:

`yarn test renderer-api_test matcher_test`

Author: jeremywiebe

Reviewers: kevinbarabash

Required Reviewers:

Approved By: kevinbarabash

Checks: ❌ Lint, flow, and coverage check (ubuntu-latest, 16.x), ✅ Test (ubuntu-latest, 16.x), ✅ Extract i18n strings (ubuntu-latest, 16.x)

Pull Request URL: https://github.com/Khan/perseus/pull/149
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