PULL_REQUEST_TEMPLATE.md

Changes proposed in this pull request:

Reviewer, please refer to this "definition of done" checklist:

• Tested on desktop (see supported browsers)
• Tested on mobile (for responsive or mobile-specific features)
• Confirm Accessibility
• Documentation is up to date
• Release notes mention the changes

⚠️ Once this pull request is merged, please merge the code into other development branches: Merge branch 'spring-18' into summer-18