Add yarn test-prod to pull request steps

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,9 +4,10 @@
 2. Run `yarn` in the repository root.
 3. If you've fixed a bug or added code that should be tested, add tests!
 4. Ensure the test suite passes (`yarn test`). Tip: `yarn test --watch TestName` is helpful in development.
-5. Format your code with [prettier](https://github.com/prettier/prettier) (`yarn prettier`).
-6. Make sure your code lints (`yarn lint`). Tip: `yarn linc` to only check changed files.
-7. Run the [Flow](https://flowtype.org/) typechecks (`yarn flow`).
-8. If you haven't already, complete the CLA.
+5. Run `yarn test-prod` to test in the production environment. It supports the same options as `yarn test`.
+6. Format your code with [prettier](https://github.com/prettier/prettier) (`yarn prettier`).
+7. Make sure your code lints (`yarn lint`). Tip: `yarn linc` to only check changed files.
+8. Run the [Flow](https://flowtype.org/) typechecks (`yarn flow`).
+9. If you haven't already, complete the CLA.
 
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